Busbars for electrically powered cells

ABSTRACT

Edge busbars on a substantial perimeter of an electrochromic device are disclosed having electrical paths wrapping over the perimeter edge. Internal busbars interior from the perimeter are disclosed which lower the conductivity of the conductive layer of an electrochromic device. Signals supplied to the busbars to control the electrochromic device are controlled by a switching power supply that allows the maintaining of the color of the electrochromic device without application of continuous power.

[0001] This application claims the benefit of U.S. Provisional PatentApplication No. 60/091,678, filed Jul. 2, 1998.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] This invention relates to busbars utilized in electricallypowered cells. In particular, this invention relates to edge andinternal busbars utilized in electrochromic devices. This invention alsorelates to edge and internal busbars that can be utilized in otherelectrically powered cells such as electroluminescent and photochromicdevices, thin-film batteries, and other cells that use geometriessimilar to the electrochromic devices described herein. Further, thisinvention relates to control circuits and methods to control thecoloration of such electrochromic devices through an intermittentapplication of power.

[0004] Electrochromic (EC) devices are devices in which a change in anelectrical signal applied to the EC device results in a change in anoptical property of the EC device. Typically, the optical property isoptical transmittance, although other properties can be affected suchas, for example, optical spectral distribution or polarization.Electrochromic devices can be used for many applications, such as rearview automotive mirrors, windows, sunroofs, shades or visors forautomotive and mass transportation applications, architectural windows,skylights, displays, light filters and screens for light pipes,displays, and other electro-optical devices.

[0005] A variety of technologies exist for producing chromogenicmembers. “Chromogenic devices”, as used herein, is employed as commonlyknown in the art. Examples of these chromogenic devices includeelectrochromic devices, photochromic devices, liquid crystal devices,user-controllable-photochromic devices, polymer-dispersed-liquid-crystaldevices, and suspended particle devices.

[0006] For example, electrochromic devices are discussed by N. R. Lynamand A. Agrawal in “Automotive Applications of Chromogenic Materials”,Large Area Chromogenics: Materials & Devices for Transmittance Control,Optical Engineering Press, Bellingham, Wash. (1989), incorporated hereinby reference. Other pertinent references include N. R. Lynam,“Electrochromic Automotive Day/Night Mirrors”, SAE Technical PaperSeries, 87036 (1987); N. R. Lynam, “Smart Windows for Automobiles”, SAETechnical Paper Series, 900419 (1990); C. M. Lampert, “ElectrochromicDevices and Devices for Energy Efficient Windows”, Solar EnergyMaterials, 11, 1-27 (1984); JP 58-20729; and U.S. Pat. Nos. 3,521,941,3,807,832, 4,174,152, 4,338,000, 4,652,090, 4,671,619, 4,702,566,4,712,879, 4,793,690, 4,799,768, Re. 30,835, 5,066,112, 5,073,012,5,076,674, 5,122,647, 5,142,407, 5,148,014, 5,239,406, and 5,657,149each incorporated herein by reference.

[0007] Electrochromic panels are also discussed by Sapers, S. P., et al.in “Monolithic Solid-State Electrochromic Coatings for WindowApplications”, Proceedings of the Society of Vacuum Coaters Conference(1996), incorporated herein by reference, with regard to devices of thetype shown in FIG. 1E. Devices comparable to that shown in FIG. 1E, andhaving photovoltaic layers for self-biasing operation are also describedin U.S. Pat. No. 5,377,037.

[0008] Other related references of interest include U.S. Patent No.5,241,411, U.K. Patent No. 2,268,595, Japanese Laid-Open Patent No.Appln. No. 63-106730, Japanese Laid-Open Patent No. Appln. No.63-106731, and U.S. Pat. No. 5,472,643, each incorporated herein byreference. Also pertinent is International Application No. PCT/US97/05791, incorporated herein by reference, which pertains toelectrochromic devices that can vary the transmission or reflection ofelectromagnetic radiation by applying an electrical stimulus to an ECdevice. International Application No. PCT/US 97/05791 uses a selectiveion transport layer in combination with an electrolyte having at leastone redox active material to provide a high-performance device.

[0009] Also suitable for use in this invention are liquid crystaldevices such as those described by N. Basturk and J. Grupp in “LiquidCrystal Guest-Host Devices and Their Use as Light Shutters”, Large AreaChromogenics: Materials & Devices for Transmittance Control, OpticalEngineering Press, Bellingham, Wash. (1989), incorporated herein byreference.

[0010] User-controllable-photochromic devices (UCPC) are discussed inU.S. Pat. No. 5,604,626, entitled “Novel Photochromic Devices”,incorporated herein by reference.

[0011] Polymer-dispersed-liquid-crystal (PDLC) devices are described byN. R. Lynam and A. Agrawal, “Automotive Applications of ChromogenicMaterials”, Large Area Chromogenics: Materials & Devices forTransmittance Control, Optical Engineering Press, Bellingham, Wash.(1989), incorporated herein by reference.

[0012] Suspended particle devices are discussed in U.S. Pat. No.4,164,365, incorporated herein by reference.

[0013] Examples of chromogenic devices that emit light are described inApplied Physics Letters, Vol. 71, page 1293 (1997).

[0014] Examples of chromogenic devices that can store image patterns dueto a change in an optical property of a material are described in U.S.Pat. No. 5,744,267, incorporated herein by reference.

[0015] The general control of chromogenic devices is discussed in U.S.Pat. Nos. 4,793,690, 4,799,768, 5,007,718, and 5,424,898, incorporatedherein by reference.

[0016] The phenomenon of prolonged coloration of chromogenic devices isdiscussed in U.S. Pat. Nos. 5,076,673 and 5,220,317, each incorporatedherein by reference.

[0017]FIGS. 1A through 1E depict typical examples of knownelectrochromic devices, while FIG. 1F shows another known type ofchromogenic device.

[0018] For example, FIG. 1A depicts a layered EC device which includes asubstrate 101, transparent conductor 103, electrochromic (redox) medium105, transparent conductor 103′ and substrate 101′.

[0019]FIG. 1B illustrates a layered EC device which includes a substrate101, transparent conductor 103, EC layer 107, electrolyte (redox medium)109, transparent conductor 103′ and substrate 101′.

[0020]FIG. 1C shows another layered EC device having a substrate 101,transparent conductor 103, EC layer 107, ion-selective transport layer111, electrolyte (redox medium) 109, transparent conductor 103′ andsubstrate

[0021] Still another such EC device is shown in FIG. 1D. This deviceincludes a substrate 101, transparent conductor 103, EC layer 107,electrolyte 113, counterelectrode 115, transparent conductor 103′ andsubstrate 101′.

[0022]FIG. 1E shows an EC device having a substrate 101, transparentconductor 103, EC layer 107, electrolyte (ion-conductive layer) 117,counterelectrode 115 and transparent conductor 103′.

[0023] A typical liquid crystal or PDLC device is shown in FIG. 1F. Thisdevice includes a substrate 201, transparent conductor 203, liquidcrystal or PDLC medium 205, transparent conductor 203′ and substrate201′.

[0024] Since the above chromogenic devices are known to those skilled inthe art, a detailed explanation of the manner of construction andoperation of such devices is not necessary.

[0025] In general, it is important to distribute the voltage to anelectrochromic (EC) device uniformly in order to (i) maintain theuniformity of the coloration and bleaching of the EC device duringchanges between such states of coloration and bleaching, (ii) to improveuniformity in such colored and bleached states, and finally (iii) toenhance the kinetics of coloration and bleaching. As the size of an ECdevice increases, it becomes increasingly more difficult to maintain thedesirable voltage distribution uniformity because increased sizetypically leads to increased resistance of various components. Suchincreased resistance results in voltage drops and current losses thatadversely affects the uniformity of voltage distribution.

[0026] In other electrical devices, a particular spatial voltagedistribution profile often is desired. As the size of such devicesincreases, similar to the example of EC devices, it also becomesincreasingly more difficult to maintain the desired spatial voltagedistribution profile because of the increasing electrical resistance ofvarious components.

[0027] An applied voltage is commonly distributed at the periphery of ECdevices through the use of an edge busbar which distributes an appliedvoltage to a surface conductor electrode. The applied voltage causes aresponse in a particular responsive property of an EC device.Consequently, spatial or temporal differences in the applied voltagewill cause spatial or temporal differences in the responsive property.Ohmic losses along an edge busbar can therefore critically affect theeven distribution of voltage, leading to undesirable non-uniformities inthe coloration and bleaching of an EC device.

[0028] Furthermore, EC devices often employ thin film transparentconductors such as indium tin oxide (ITO) and doped tin oxides (DTO) forthe surface conductor electrode. Such thin film transparent conductorsare also used in a wide range of applications in other areas such asdisplays, solar cells, and liquid crystal devices. If the magnitude ofthe electrical currents in such devices is large, there can be aconsiderable electrical potential drop across the transparent conductor.Similar to the effect of voltage variations along an edge busbar,variations of voltage in thin film transparent conductors can also leadto spatial inhomogeneities in the device behavior as well as to sloweroverall device kinetics. Such effects become increasingly noticeable andproblematic with increasing device area.

[0029] Another related aspect of electrochromic devices is that they arecurrent consuming devices. Accordingly, it is advantageous for thetransparent conductors, i.e., the surface electrodes, to be veryconductive. For applications such as large area EC panels, where currentconsumption is large, it is particularly important that the transparentconductors possess high effective conductivities. Present conventionallarge-area EC devices fabricated from commercially available transparentconductors such as, for example, ITO and DTO, generally possess slowkinetics and often display nonuniform coloring. For example, large-areaEC devices presently are often darker at the edges than in the center.

[0030] EC devices can be fabricated on one substrate as described inU.S. Pat. No. 4,712,879; J. Gordon H. Matthew et. al., Proc. of 3dSvmposium on Electrochromic Materials, The Electrochemical Society,Proc. Volume 96-24, Pennington, N.J., 1997, p. 311; and Badding, M. E.,et al., Proc. of 3d Symposium on Electrochromic Materials, TheElectrochemical Society, Proc. Volume 96-24, Pennington, N.J., 1997, p.369, each incorporated herein by reference.

[0031] Electrochromic devices can also be made using two substrates asdescribed in U.S. Pat. Nos. 4,761,061, 4,768,865, 4,902,108, 5,142,407,5,231,531, 5,472,643, and U.S. patent application Ser. No. 09/155,601,filed Aug. 9, 1997, each incorporated herein by reference.

[0032] Prior art EC devices are also described in Lynam N. R., Agrawal,A., Automotive Applications of Chromogenic materials, in Large-AreaChromogenics: Materials and Devices for Transmittance Control, SPIEOptical Engineering Press, Bellingham, Wash., 1990, p. 46 and Lampert C.L., Selkowitz, S. E., Large-Area Chromogenics: Materials and Devices forTransmittance Control, SPIE Optical Engineering Press, Bellingham,Wash., 1990, p. 22, each incorporated herein by reference.

[0033] U.S. Pat. Nos. 5,202,787 and 5,151,824, each incorporated hereinby reference, show the way busbars in an EC device are typically put onthe substrate edges in the prior art. As shown in FIGS. 2, 3A, and 3B,taken from the referenced patents, in a commercial EC automotive mirrorwhich features two substrates 2223 and 2224, or 3333 and 3334, thesubstrates are staggered slightly with respect to each other. Springclips 2221 and 2222, or 3331 and 3332, of a conductive material such asa copper sheet or a beryllium copper coated with tin are clipped to thetwo staggered edges of substrates 2223 and 2224, or 3333 and 3334, inorder to provide an electrical connection to substrates 2223 and 2224,or 3333 and 3334. The two substrates must be offset, or staggered, fromeach other in order to expose surfaces 2225 and 3335 for the attachmentof clips 2221 and 2222, or 3331 and 3332. The surfaces 2225 and 3335 areminimized in order to maximize the optical throughput area of thedevice—that is, to maximize the overlapping area of the two substrates.Accordingly, the prior art provides electrical connections at less thanone half of the perimeter of each substrate.

[0034] When a potential is applied to the wire clips 2221 and 2222, or3331 and 3332, only a small potential drop occurs in these clips becauseof their high conductivity. The small potential drop can be neglectedfor small dimensions. However, as the dimensions of the applicationincreases, the potential drop can become significant. Such potentialdrops can be a problem because the potential drop comes at a cost to thepotential available to the chromogenic elements themselves. Further,significant current flow can occur at the clips and clip junctions,thereby adversely adding to the overall current load.

[0035] The resistance of a typical wire clip used in commercialautomotive mirrors that are about 12 inches (30 cm) in length is about0.29. The conductivity associated with the clip depends on the intrinsicconductivity of the material, the geometric parameters of the clip (suchas thickness, width and the length of the strip), and on the relevantcontact resistance.

[0036] To demonstrate the current consumption in the EC devices, acommercial EC automotive mirror was colored by applying a DC stepvoltage of 1.4 V. The mirror initially consumed a current of 3 mA/cm²,decreasing to 0.9 mA/cm² in the fully colored state.

[0037] According to Hichwa, B.P1, “Large Area Electrochromics forArchitectural Applications”, International Conference on Coatings onGlass, Saarbrucken, Germany, October 1996, an EC window device made fromall thin films on a single substrate when powered at 1.8 V showed aninitial current consumption of about 2 mA/cm² which decreased to about 1μA/cm² in the colored steady-state. By assuming that such devices can befabricated with the above current values scaling with size while keepingsimilar performance characteristics, the current consumption can becalculated for an EC automotive mirror and a single substrate EC windowat different dimensions.

[0038] Table 1 shows the current consumption of the devices with twodifferent active areas: (1) 6 inches by 6 inches (15 cm×15 cm) and (2)12 inches by 12 inches (30 cm×30 cm). TABLE 1 Colored (steady DeviceInitial current state) current type/Size consumption consumption AutoMirror, 0.7 A 0.2 A 6 inch (15 cm) Thin film 0.5 A 0.2 mA window, 6 inch(15 cm) Auto Mirror, 2.8 A 0.8 A 12 inch (30 cm) Thin film 1.9 A 0.9 mAwindow, 12 inch (30 cm)

[0039] Therefore, as the size of the EC device increases, the currentloads that the electrodes must carry are substantially increased.

[0040] Table 2 shows the resistance characteristics of several materialsand the resistance associated with a tape with a dimension of 1 meter inlength, 2 mm in width and 0.1 mm in thickness. Table 2 also shows theresistance drop in these tapes when they carry 0.1, 1 and 10 A ofcurrent. TABLE 2 Data for one m long tape with a width of 2 mm and athickness of Resist- 0.1 mm ivity Resis- Voltage Voltage Voltage at 25°C. tance drop at drop at Drop at Material (10⁻⁸Ωm) (Ω) 0.1A (v) 1A (v)10A (v) Aluminum 2.71 0.1355 0.01355 0.1355 1.355 Copper 1.71 0.08550.00855 0.0855 0.855 Gold 2.21 0.1105 0.01105 0.1105 1.105 Silver 1.620.081 0.0081 0.081 0.81 Tungsten 5.39 0.2695 0.02695 0.2695 2.695 ITO200 10 1 10 100 Stainless 72 3.6 0.36 3.6 36 steel type 304 Tin 11.50.575 0.0575 0.575 5.75 Copper/ beryllium (98/2) Indium 8 0.4 0.04 0.4 4Nickel 7.12 0.356 0.0356 0.356 3.56 Rhodium 4.3 0.215 0.0215 0.215 2.15Nichrome 150 7.5 0.75 7.5 75 Solder 16 0.8 0.08 0.8 8 (Pb/Sn, 67/33)Solder 25 1.25 0.125 1.25 12.5 (Sn/Ag, 95/5) Conduct- 300 15 1.5 15 150ive epoxy Ablebond ® 8380 Silver 7 0.35 0.035 0.35 3.5 Frit (DuPont,1991)

[0041] As seen in Table 2, several materials incur serious voltage dropsacross their resistance runs (for a specific geometry) for the amount ofcurrent that must be provided to the EC cell. Since EC devices aretypically powered at 1 to 3 volts, the voltage drop can significantlyaffect the actual voltage applied to the EC material, causing increasesin coloration and bleach times, and in certain devices, leading tononuniform coloration in the steady state condition. The problem of thevoltage drop, resulting from the electrode resistance, is compounded bythe increase in current when the size of the device gets larger as seenpreviously in Table 1. This invention is particularly useful for thoseEC devices where the current consumption exceeds 0.1 A during eithercoloring or bleaching processes.

[0042] When chromogenic devices are fabricated using two coatedsubstrates, the typical gap between the substrates is in the range offrom 10 to 1000 micrometers. As the size of the devices increases, suchas for a six inch by six inch (15 cm×15 cm) device, in order to increasethe charge throughput and to distribute the charge uniformly, it isimportant that busbars be applied to as much of the device perimeter aspossible.

[0043] One prior art approach for a rectangular device as shown in FIG.4, is to offset substrates 3301 and 3302 simultaneously around two edgesof a corner to provide two exposed L-shaped surfaces 3304. Then, busbars3303 are attached in a conventional way.

[0044] In another prior art approach, busbars 5503 are applied onopposite edges of exposed surface pairs 5504 by employing the geometryas shown in FIG. 5 where the rectangular substrates 5501 and 5502 arepivoted from each other so that the long dimension of each rectangularsubstrate is parallel to the short dimension of the other rectangularsubstrate.

[0045] Neither approach provides busbar coverage of a substantialperimeter of a substrate. As used herein, “substantial perimeter” meansmore than half of the perimeter of a substrate which is covered by acontinuous busbar. For larger devices such as those bigger than about 6inches (15 cm) in width and length, it is especially desirable to putthe busbars all around the device, in a manner which covers asubstantial perimeter of each substrate in order to provide the appliedsignal to the entire chromogenic panel evenly.

[0046] Nevertheless, as described above, as the length of the busbar runincreases, the resistance undesirably increases. As a result, the priorart increases the thickness of the busbar material for large devices inorder to increase the conductivity/unit length of the busbar in anattempt to maintain the desirably low resistance of the busbar. However,a major problem with the use of conventional busbars such as springclips and wires for such large chromogenic applications arises when thethickness of the busbar exceeds the typical cell gaps. Even when thethickness of the busbar does not exceed the cell gap, the geometries ofthe prior art busbars and their placement limit the allowable increasesto conductivities. Further, there may also be a problem around substratecorners when one continuous strip of the prior art busbar clip is used.

[0047] Another method with substantial coverage is provided all aroundthe periphery, by using thin conductors, as shown in U.S. Pat. No.5,066,112. However, in this case, the conductor thickness is limited bythe gap between the substrates and its width.

[0048] Another approach is to make the two substrates dissimilar in sizeso that the edges of one substrate extend from all around the perimeterof the other substrate. In this configuration, conventional wire clipbusbars can be used on the larger substrate. However, it is difficult toattach conventional wire clip busbars to the smaller substrate due tothe limited gap available between the two substrates. The very closegeometry could cause electrical shorting of the two substrates at theconventional wire clip busbar of the smaller substrate.

[0049] As noted above, in addition to the problem of voltage drops fromthe edge busbar clips, if the magnitude of the electrical currents in ECdevices is large, there can be a considerable electrical potential dropacross the thin film transparent conductor, leading to detrimentallyslower overall device kinetics and spatial inhomogeneities in the ECdevice behavior. Therefore, for applications where current consumptionis large, and especially where the area of the EC devices is large(e.g., chromogenic panels), it is particularly important that thetransparent conductors possess large effective conductivities.Large-area EC devices fabricated from commercially available transparentconductors such as, for example, indium tin oxide (ITO) and doped tinoxide (DTO) generally possess slow kinetics and often display nonuniformcoloring (e.g., darker at the edges to which the busbars are connectedthan in the center).

[0050] Values for the sheet resistance of commercially availabletransparent conductors such as ITO and DTO are typically greater thanabout 5 Ω/sq (the units are also commonly written as Ω/▪) to about 15Ω/sq. Lower sheet resistances may be obtained by increasing thethickness of the transparent conductor, but this adversely affects theoptical properties (e.g., increased haziness and/or diminishedtransmissivity) and also adds appreciably to the cost. It is desirableto form substrates which possess appreciably lower effective sheetresistance (can be less than 1 Ω/sq) at a cost that is attractive forapplications such as those described above.

[0051] U.S. Pat. No. 5,293,546, incorporated herein by reference,describes a method for making a display device in which one of theelectrodes is preferably a metallic grid. Preferred line widths were 20micrometers with line spacings of 500 micrometers and line heights of0.2 to 3 micrometers. The grid is then coated by a metal oxide (e.g.,1000 Å of ITO). The invention relates to displays in which highresolution processing equipment must be used for depositing the gridpattern. Thus the cost is high, particularly if large substrates such as6 inch−6 inch (15 cm×15 cm) or bigger are required because maintaininghigh precision in such a fine grid pattern over increasing areas iscostly. Further, since these substrates must be over-coated with ITO,they are unable to use more cost effective, mass produced transparentconductors, such as mass produced ITO or inexpensive DTO deposited ontoglass sheets in a float line.

[0052] U.S. Pat. No. 4,768,865, incorporated herein by reference,describes the use of a free-standing metallic grid as one of thetransparent conductors. In this invention, the metal grid participatesdirectly in the electrochemical reaction in the EC cell. However, formost EC devices, it is not desirable for the electron conductor also toparticipate in the reaction.

[0053] U.S. Pat. No. 5,724,176, incorporated herein by reference,describes the use of a counterelectrode for a smart window that containsa transparent substrate and a linear electrically conductive materialformed on a surface of the transparent substrate. A layer of anelectrochromic material is formed on the window's surface, and a layerof an electrolyte is arranged between the counterelectrode and theelectrochromic electrode and in contact with the layer of theelectrochromic material. Various patterns are described for theplacement of the linear electrically conductive material.

[0054] U.S. Pat. No. 5,066,111, incorporated herein by reference,describes laminated EC devices. A metal grid on a glass substrate isemployed as one electrode and a longitudinal set of busbars, preferablycomposed of a metal foil such as copper, or an electroconductive ceramicfrit deposited on glass or on the surface of an electro-conductive film,is employed as the other electrode. The electrochromic film is depositedover the second electrode. Thus, the metal foil or frit conductors ofthe U.S. Pat. No. 5,066,111 invention are always in direct contact witheither the electrochromic coating or the electrolyte. However, suchdirect contact can decrease the device lifetime because of reactionbetween the coating and the electrolyte or electrochromic coating.Moreover, if put on glass and then coated with the transparentconductive coating (TCC), other problems can arise. Most importantly,the TCC is usually deposited in a thickness of less than 0.3micrometers. In comparison, tapes or underlying frits, etc., aretypically in thicknesses of 10 to 1000 times the thickness of TCC. Thus,vacuum methods that are typically used to coat TCC have difficultygetting a conforming coating that adequately covers the edges. Thereference does not address the relationship of the busbar thickness andwidth to the device size.

[0055] POLYCHROMIC™ solid films are described in European PatentPublication No. EP 0 612 826 A1, incorporated herein by reference. Thereference describes how polychromic solid films may be used inelectrochromic devices, particularly glazings and mirrors, whosefunctional surface is substantially planar or flat or that are curvedwith a convex curvature, a compound curvature, a multi-radius curvature,a spherical curvature, an aspheric curvature, or combinations of suchcurvature.

[0056] Often, a demarcation means, such as a silk-screened or otherwiseapplied line of black epoxy, may be used to separate the more curved,outboard blind-spot region from the less curved, inboard region of suchelectrochromic mirrors. The demarcation means may also include anetching of a deletion line or an otherwise established break in theelectrical continuity of the transparent conductors used in such mirrorsso that either one or both regions may be individually or mutuallyaddressed. Optionally, this deletion line may itself be colored black.Thus, the outboard, more curved region may operate independently fromthe inboard, less curved region to provide an electrochromic mirror thatoperates in a segmented arrangement. As described in European PatentPublication No. EP 0 612 826 A1, upon the introduction of an appliedpotential, either of such regions may color to a dimmed intermediatereflectance level, independent of the other region, or, if desired, bothregions may operate together in tandem.

[0057] An insulating demarcation means, such as demarcation lines, dotsand/or spots, may be placed within electrochromic devices, such asmirrors, glazings, optically attenuating contrast filters and the like,to assist in setting out the interpane distance of the device and toenhance overall performance, in particular the uniformity of colorationacross large area devices. Such insulating demarcation means,constructed from, for example, epoxy coupled with glass space beads,plastic tape or die cut from plastic tape, may be placed onto theconductive surface of one or more substrates by silk-screening or othersuitable technique prior to assembling the device. The insulatingdemarcation means may be geometrically positioned across the panel, suchas in a series of parallel, uniformly spaced-apart lines, and may beclear, opaque, tinted, or colorless, and appropriate combinationsthereof, so as to appeal to the automotive stylist.

[0058] As described in European Patent Publication No. EP 0 612 826 A1,a demarcation means may be used that is conductive as well, providedthat it is of a smaller thickness than the interpane distance and/or alayer of an insulating material, such as a non-conductive epoxy,urethane or acrylic, is applied thereover so as to prevent conductivesurfaces from contacting one another and thus short-circuiting theelectrochromic assembly. Such conductive demarcation means includeconductive frits, such as silver frits like the #7713 silver conductivefrit available commercially from E.I. du Pont de Nemours and Co.,Wilmington, Del., conductive paint or ink and/or metal films. Use ofconductive demarcation means, such as a line of the #7713 silverconductive frit, having a width of about 0.09375″ (0.238 cm) and athickness of about 50 μm, placed on the conductive surface of one of thesubstrates of the electrochromic device may provide the added benefit ofenhancing electrochromic performance by reducing busbar-to-busbaroverall resistance and thus enhancing uniformity of coloration, as wellas rapidity of response, particularly over large area devices. However,the non-conductive layers are applied in a way which does not preventthe underlying frit lines from making contact with the electrolyte orelectrochromic layers. Thus, this frit may potentially react, especiallywhen coloring and bleaching potentials are applied.

[0059] As described above, electrochromic (EC) devices are used toreversibly vary the light transmission or reflection by application ofan electrical voltage. Applications of electrochromic devices includewindows for architectural use (windows, interior partitions, skylights,light pipes), windows in transportation (automobiles, trucks, planes,trains, boats, etc.), eye-wear, and displays (including large areasignage).

[0060] Electrochromic windows in buildings can provide higher energyefficiency as compared to static transmission windows, while increasingthe user comfort by controlling illumination and reducing glare. Thesame benefits can accrue for transportation uses where the user comfortis enhanced by reducing solar heat and glare during the day, whilereducing the cooling load on the air-conditioner. In many of theseapplications the EC device can be required to be kept in a certaindesired state of transmission for long periods of time. For example, awindow may be kept in a darkened or bleached state for many hours of theday and may even be kept in this state for many days.

[0061] Thus, it is desirable to enhance the durability of EC devicesthat are used in this long single state mode, while reducing energyconsumption of the EC devices. Reducing energy consumption isparticularly useful in circumstances where solely a battery is used topower such a device and thus, it is important to ensure that the batterydrain is minimized. Such circumstances include use in a car, aircraft,watercraft, or eyeware. One aspect of the present patent describescircuitry which addresses one or more of these issues.

[0062] U.S. Pat. No. 5,148,014, incorporated herein by reference,describes the use of a linear regulated power supply to power an ECmirror.

[0063] U.S. Pat. No. 5,193,029, incorporated herein by reference,describes the use of a Zener diode and transistor, which is essentiallya linear regulation, to provide voltage to an EC mirror.

[0064] U.S. Pat. No. 5,220,317, incorporated herein by reference,describes the use of a voltage divider consisting of series resistors toscale down the voltage provided to EC elements.

[0065] Electrochromic devices which will benefit from this invention arewell known in the art. For example, these are described in U.S. patentapplication Nos. 09/155,601 and 08/699,940, filed Apr. 9, 1997 and Aug.20, 1996, respectively.

[0066] For those EC devices which are colored by applying a voltage, itwould be desirable not to require applying continuously the coloringpotential after the required coloration depth has been reached. Suchcontinued application of the coloring potential, while promoting ECreactions, can also promote side reactions which could have detrimentaleffect on the device longevity. This applies for all EC devices whichneed to be maintained in a state of coloration that is different fromtheir natural transmission state. The natural transmission state of anEC device is measured at equilibrium with no applied potential and whenthe potential difference between the opposing electrodes is zero.

[0067] Typically, the EC devices can be kept colored for a finite periodof time when the coloring potential is removed, i.e., the color of thedevice will change towards its natural state over a period of time. Thischange could occur over a wide range of time intervals, from fast overseveral seconds or minutes, to as slow as extending up to many days,depending on the device. A device where this change is fast is said tohave short “memory” and one where the change is slow is said to possesslong “memory”. For example, U.S. patent application No. 09/155,601discloses devices with long memories and compares them with devices thathave short memories.

[0068] It is clear that is would be advantageous to be able to maintaina coloration setting without having to maintain an applied voltage toelectrochromic devices because circuitry that allows intermittentadjustment of the voltage as needed to maintain a coloration settingwould lead to lower Dower consumption in the device.

[0069] U.S. Pat. No. 5,384,578 (to Lynam et.al.), incorporated herein byreference, describes the use of intermittent voltages for continuouslyvariable mirror and windows, but does not relate to changing thevoltage-on or voltage-off periods and voltage-time shapes underdifferent conditions as discussed in the present invention.

[0070] U.S. Pat. No. 4,298,970 (to Saegusa), incorporated herein byreference, describes a technique for utilizing an intermittent techniqueto drive EC displays with memory. The patent only describes bimodaldisplays which have only two states, i.e., colored and bleached statesand does not discuss devices which need continuously variable lighttransmission across a continuum of transmissive states.

[0071] U.S. Pat. No. 5,007,718, incorporated herein by reference,describes a method of driving electrochromic elements by using a currentstabilizing circuit and a voltage stabilizing circuit in tandem with apower supply to form a stabilized power source, and applying a graduallyincreased coloring voltage and a gradually decreased discoloring voltageto keep the current flow within predetermined amounts.

[0072] U.S. Pat. No. 5,365,365, incorporated herein by reference,describes an electrochromic system for controlling the color state bydetermining the charge needed to obtain a set color from the dischargepotential of the system and the coloration set-point. An integratormeasures the charge passing through the system and compares it to thecharge to be transferred, which is measured by a differential amplifierwhich compares a discharge potential measured by a capacitor with aselected color set-point.

[0073] U.S. Pat. No. 5,231,531, incorporated herein by reference,describes an electrochromic system in which a voltage generator isconnected to electrically conductive films by an electrical controlcircuit. The voltage generator receives a set-point from a control unitand generates a potential differences as a function of the temperatureof the electrolyte.

SUMMARY OF THE INVENTION

[0074] This invention is related to edge and internal busbars that lowerthe overall effective resistance of electrical devices, particularly ECdevices, thereby enabling large devices to maintain desirable electricalproperties. The present invention describes the benefits of applying thebusbars of the present invention to a substantial perimeter of an ECdevice, as well as the materials and processes to accomplish this.

[0075] As shown later, the contact points with the conductive coatingsconstituting the EC devices may be less than half of the perimeter, butthe busbar of the present invention runs continuously for more than halfof the device perimeter. The term “busbar” refers to a conducting mediumthat provides a substantially uniform voltage to all those points on thedevice perimeter that are connected to the busbar. The busbar should becapable of carrying substantial current with a voltage drop ofpreferably less than {fraction (1/10)}th of the applied voltage, or avoltage drop less than that which causes a perceptible change in thekinetics of the device (rate of coloration and bleach) or in the depthof coloration.

[0076] The voltage drop should be less than that voltage drop whichwould cause a perceptible change in the kinetics or colorationproperties of the device. Thus, for some particular devices, highervoltage drops can be accommodated so long as such perceptible changes donot occur. Generally, however, such voltage drops are less than{fraction (1/10)}th of the applied voltage.

[0077] The conductance of the edge busbar conductor is dependent on thecross-section, length and the intrinsic conductivity of the busbarmaterial. Since the gap between the two substrates for a EC cell islimited, the thickness of the busbar conductors must be within thelimitations imposed by the cell's size. To maximize the EC deviceviewing area, the width of the conductor in the prior art is limited asshown in FIGS. 4 and 5, where the width is limited to the exposed areas3304 and 5504. Typically, this width is less than 25 mm, preferably lessthan 10 mm, in order to maximize effective cell area. At times, thiswidth can be on the order of less than 2 mm. Further, for a device madeby substrates that are exactly stacked on one another and separated by agap of 100 micrometers, the thickness of the conductor on each substratelocated between the two substrates is typically limited to less than 50micrometers.

[0078] The present invention teaches the use of materials and processesto deposit busbars on a substantial portion of the device perimeterwhile overcoming the geometric constraints described above. A copperconductor which is 35 micrometers thick and 3 mm wide exhibits aresistance drop of 0.16Ω per meter. Accordingly, for a device that isone meter square, a continuous conductor around the device peripherywill exhibit a drop of 0.32Ω from one diagonal edge to the other. For adevice that will carry a current as low as even one ampere, the drop of0.32 V at an applied potential of about 1.5 V is significant. This canresult in non-uniform coloration, slow kinetics, etc. In such devices,it is preferable to maintain the potential drop below {fraction(1/10)}th of the applied voltage or below any voltage that will cause aperceptible change in the color uniformity of the device or a decreasein the kinetics.

[0079] Since the current consumption of an EC device changes with time,particularly when step potentials are used, it is preferable that thepotential drop in the busbar is kept within the limits described aboveduring both the switching period and also when the steady state isreached. If other materials from Table 2 are used instead of copper,except for silver, the resistance drop will be even higher for the samebusbar dimensions. Thus the geometry of the busbar (such as thicknessand width) of the tape will have to be increased for best performance.

[0080] An object of the present invention is to overcome the prior artconstraints on edge busbar effective resistance arising from thegeometrical limitations of busbar length, width, and thickness. Thepresent invention uses specific geometry, materials and processes toform the edge busbars.

[0081] This invention overcomes these geometrical limitations by forminga conductive path from the electrode on a front side of a substrate tothe edges of the substrate and then extending this conductive path on tothe back of the substrate. On the edge of the device, on the back, or onboth the edge and the back, highly conductive paths such as reinforcingconductors may be employed to lower the busbar resistance. Theconductive path from the front of the substrates to the back could bethe continuation of the same material which is used for the transparentconductor, such as indium tin oxide, or can be fabricated from adifferent material, so long as dimension and conductivity requirementsare met. That is, the conductivity must be effective to prevent apotential drop of 10% or a potential drop that would detrimentallyaffect the performance of the EC panel, while the dimensions must beeffective to allow the substrates to maintain a close proximity to eachother. Once the conductive path is formed on the back of the substrates,the geometrical limitations on the thickness and the width of the busbarconductor are relieved substantially.

[0082] Accordingly, the present invention provides an edge busbar for anelectrical device, wherein the edge busbar comprises at least oneelectrically conductive connector portion effective to form anelectrically conductive path from a surface of the electrical device,wrapping around a portion of an edge, to an opposite surface of theelectrical device, and an electrically conductive perimeter portion inelectrical contact with the connector portion, wherein the perimeterportion is peripherally on a substantial perimeter of the electricaldevice.

[0083] The connector portion of the edge busbar of the present inventioncan be continuous peripherally on a substantial perimeter of theelectrical device, can be continuous peripherally on an entire perimeterof the electrical device, or can be composed of a plurality of connectorportions. That is, the connector portion can wrap completely around anentire perimeter edge of the electrical device, can wrap completelyaround a substantial perimeter portion of the perimeter of theelectrical device, or it can be a series of smaller portions that eachwrap around smaller portions of the perimeter of the electrical device.Regardless, there is a perimeter portion of the edge busbar of thepresent invention which is peripherally on a substantial perimeter ofthe electrical device and connects to the various connector portion(s)of the present invention.

[0084] The front of a substrate is generally defined as the surfacehaving the conductive electrode layer thereon.

[0085] In the case of a two substrate device, the front of a substrateis the surface facing the other substrate. In the case of a singlesubstrate EC device, the front of a substrate is the surface facing theEC stack. In general, the layer of transparent conductive material is onthe front of a substrate.

[0086] Although other parameters such as the conductivity of thetransparent conductors (electron conductors), the ionic conductivity ofthe electrolyte layer, and the intercalation rate in the EC coating andother coatings if used, might also influence the kinetic parameters ofEC devices, as shown above, the resistance of the edge busbar itself canhave an important affect on the performance of the EC device.Accordingly, it is an object of the present invention to minimize thecontribution of the edge busbars towards slowing the EC device kinetics.The edge busbars of the present invention may also assist in promoting aspatially uniform rate of color change during coloring and bleachingcycles.

[0087] In one embodiment of the present invention, an edge busbarincludes a connector portion that has a separation or separatingportion. However, the connector portion at each side of the separationis electrically connected by the conductive electrode coating layer ofthe electrical device. The separation is relatively small between theconnector portions on each side of the separation, so that there isnegligible resistance across the break. In other words, the separationis electrically bridged by the conductive electrode coating layer. Thisallows the connector portion to be effectively continuous peripherallyabout the entire perimeter of the electrical device even thoughseparations exist in the connector portion. Advantages to thisconfiguration include ease of manufacture and reduced complexity ofdesign.

[0088] Busbars of the present invention can be advantageously used inpairs. Another embodiment of the present invention provides an edgebusbar pair for an electrical device, each edge busbar comprising aconnector portion and a perimeter portion, wherein each connectorportion is effective to form an electrically conductive path from afront surface of a substrate, wrapping around a portion of an edge ofthe substrate, to an opposite back surface of the substrate. Theperimeter portions being in electrical contact with its respectiveconnector portion, and wherein each perimeter portion is peripherally ona substantial perimeter of each respective substrate, and wherein thefront surfaces of each substrate face each other with each substantialperimeter proximate to and substantially opposite to the othersubstantial perimeter.

[0089] As discussed previously, each edge busbar of an edge busbar paircan be continuous peripherally on a substantial perimeter of itssubstrate, can be continuous peripherally on an entire perimeter of itssubstrate, or can be composed of a plurality of connector portions. Itis advantageous for each edge busbar to be composed of a plurality ofconnector portions. It is particularly advantageous for each connectorportion of each edge busbar to be in an alternating relation withconnector portions of the other edge busbar. As shown later, when theconnector portions are in such alternating relation, the thickness ofthe busbar material can be thicker than one half of the total gapdistance between the substrates and yet still not cause an electricalshort. Further, a sealant and/or an insulator can be added to assureagainst any shorting. Nonetheless, as explained earlier, thicker busbarmaterial is desirable in order to maximize conductivity.

[0090] The present invention can be implemented for single substratedevices or dual substrate devices. The edge busbars of the presentinvention can be used singly as needed advantageously (as contrastedwith the prior art). However, single substrate devices can nonethelessrequire a pair of edge busbars because such devices, as describedearlier and as known in the art, often are made by forming an EC stackonto a substrate. In such cases, the EC stack requires a pair conductiveelectrodes as well as the substrate. Accordingly, both conductiveelectrodes have electrical signals applied to them which would benefitfrom the advantages of the edge busbars of the present invention.

[0091] In the present invention, an edge busbar is used having a portionthat can be fabricated of any convenient material with an effectivemaximum thickness that can be inserted in the cell gap without shortingfrom touching with the other busbar or with the opposing conductivesubstrate. At the same time, the edge busbar of the present inventionprovides sufficient conductivity such that a negligible voltage drop(preferably less than one tenth of the applied voltage) occurs in theedge busbar. Further, the edge busbar of the present invention covers asubstantial portion of the device perimeter and can include the internalbusbars of the present invention.

[0092] The present invention also relates to the construction ofsubstrates, especially transparent conducting substrates, which possessrelatively large effective conductivities by the inclusion of internalbusbars.

[0093] The present invention further relates to the use of theaforementioned substrates to construct affordable large area EC devicesthat can be used for architectural applications, (e.g. windows,partitions, skylights, diffuser panels, light pipes, etc.), automotive(windows, sunroofs, etc.) or other transportation (windows for planes,trains, buses, boats, etc.) applications, or signage applications(including large area displays such as those used at stock exchanges,airports and other such facilities).

[0094] The present invention also provides substrates which possessappreciably lower effective sheet resistances (can be less than 1 Ω/sqor Ω/▪) at a cost that is attractive for applications such as thosedescribed above.

[0095] The present invention teaches means for lowering the sheetresistance of thin film transparent electrically conducting assembliesfor use in chromogenic devices, particularly electrochromic (EC)devices. The present invention permits the manufacture of EC deviceswhich possess significantly improved kinetics with regard to colorationand/or bleaching, even for devices which possess relatively large activeareas. The present invention also results in devices which possessconsiderably improved coloration and bleaching uniformity.

[0096] Most practical EC devices, as shown in FIG. 6, are comprised ofan “EC Assembly” 6601 which is effectively bound on either side byelectronically conducting electrodes (ECE) 6602. Generally speaking,electrodes 6602 may be comprised of any of a variety of electronicconducting materials. Because EC devices are generally used to modulatelight, however, at least one of the ECE 6602 should possess reasonabletransparency at the wavelengths of interest (mirrors and many displays,e.g., typically possess only one transparent ECE; and window-typedevices typically possess two transparent ECE's). The present inventionprovides improved effective conductivity of transparent ECE's in amanner readily integrated into the device structure.

[0097] The present invention forms internal busbars by providing stripsof highly conductive material electrically connected to interiorportions of a transparent ECE. The internal busbars add regions ofincreased conductivity into a transparent ECE, thereby lowering theoverall effective resistance of the transparent ECE. Such loweredoverall resistance leads to large device advantages.

[0098] The internal busbars of the present invention have increasedconductivity compared to the transparent ECE when measured along thelongitudinal direction of the conductive strips of the presentinvention. That is, in a top view of the transparent ECE with aninternal busbar strip, when one compares a section of the conductivestrip having a length L and a width W with a section of the transparentECE also having the dimensions of W×L, the conductivity of the W×Lsection of the internal busbar will be higher than the conductance ofthe W×L section of the transparent ECE, along either dimension L or W.Preferably the conductivity of the conductive strip will be greater thanabout 2 times the conductivity of the transparent ECE, more preferablygreater than about 10 times.

[0099] The internal busbars of the present invention achieves suchhigher conductance by several ways. According to one embodiment of thepresent invention, materials having inherently higher conductivities areused for the busbars. According to another embodiment of the presentinvention, the busbar strips are made thicker than the surroundingtransparent ECE. Such thicker strips can be embedded below thetransparent ECE and/or into the underlying substrate. It is importantthat these two—that is, the internal busbars and the transparent ECE—arein electrical contact with each other (continuous or spatiallyintermittent). One may even use a material, to enhance or to tailor theelectrical characteristics of this electrical contact, different fromthat material of the internal busbars or of the transparent ECE.

[0100] In another embodiment, the internal busbar strips are formed on adifferent surface from that surface which has the transparent ECE. Stripconnecting portions connect interior portions of the transparent ECE ordevice with segments of the internal busbar strip. Such strip connectingportions can extend through the substrate. The internal busbars of thisembodiment are nonetheless “internal” because they connect to regions ofthe transparent ECE away from the periphery.

[0101] The present invention also is directed to circuitry which useslow power. Another object of the present invention are circuits whichapply intermittent coloration power to EC devices in order to maintainor control the EC devices' coloration while compensating for the ECdevices' inherent coloration decay without needing a constantapplication of coloration power.

BRIEF DESCRIPTION OF THE DRAWINGS

[0102]FIGS. 1A, 1B, 1C, 1D, 1E, and 1F are side cross-sectional views ofa number of different prior art electrochromic, liquid crystal, PDLC,and photochromic devices suitable for use in the present invention.

[0103]FIG. 2 is a perspective view of a prior art arrangement of edgebusbars clips on two substrates.

[0104]FIG. 3A is an perspective exploded view of a prior art arrangementof edge busbar clips on two substrates.

[0105]FIG. 3B is a sectional view of a prior art arrangement of edgebusbar clips on two substrates.

[0106]FIG. 4 is a perspective view of a prior art arrangement of edgebusbars clips on two substrates.

[0107]FIG. 5 is a perspective view of a prior art arrangement of edgebusbars clips on two substrates.

[0108]FIG. 6 is a schematic side view of an EC device.

[0109]FIG. 7A is a schematic sectional view of an EC device having edgebusbars of the present invention.

[0110]FIG. 7B is a schematic sectional view of an EC device having edgebusbars and conductive paths of the present invention.

[0111]FIG. 8A is a perspective view of an EC device with a substratehaving edge busbars of the present invention.

[0112]FIG. 8B is a schematic top plan view of a substrate having acontinuous conductive path of the present invention.

[0113]FIG. 8C is a schematic top plan view of a substrate having stripconductive paths of the present invention.

[0114]FIG. 9A is a schematic side view of a pair of edge busbars of thepresent invention.

[0115]FIG. 9B is a schematic side view of an adhesive multilayer stripfor the fabrication of an edge busbar of the present invention.

[0116]FIG. 9C is a plan view of an adhesive multilayer strip for thefabrication of an edge busbar of the present invention.

[0117]FIG. 9D is a perspective partial view of a pair of edge busbars ofthe present invention at a corner.

[0118]FIG. 10 is a schematic cross sectional view of a pair of edgebusbars of the present invention.

[0119]FIG. 11A is a side view of a prior art stacked substratearrangement.

[0120]FIG. 11B is a top view of a prior art stacked substratearrangement.

[0121]FIG. 12 is a schematic side sectional partial view of a prior artstacked substrate arrangement.

[0122]FIG. 13 is a perspective view of a single substrate with a bottomconductor applied according to an embodiment of the present invention.

[0123]FIG. 14 is top view of a single substrate with a top conductorapplied according to an embodiment of the present invention.

[0124]FIG. 15A is a schematic sectional side view of a single substratewith a top and bottom conductors applied according to an embodiment ofthe present invention.

[0125]FIG. 15B is a schematic sectional side view of a single substratewith a top and bottom conductors applied according to an embodiment ofthe present invention.

[0126]FIG. 15C is a schematic sectional side detail view of a substratewith a bottom conductor and signal connections according to anembodiment of the present invention.

[0127]FIG. 16A is a schematic sectional side view of a single substratewith embedded edge busbars according to an embodiment of the presentinvention.

[0128]FIG. 16B is a schematic sectional side view of a single substratewith embedded edge busbars according to an embodiment of the presentinvention.

[0129]FIG. 17A is a top view of a substrate with a continuous conductorbusbar according to an embodiment of the present invention.

[0130]FIG. 17B is a perspective view of a substrate with a continuousconductor busbar according to an embodiment of the present invention atan intermediate fabrication step.

[0131]FIG. 18 is a graph of the light transmittance vs. time fordifferent busbar configurations according to the present invention.

[0132]FIG. 19A is a schematic sectional view of a stacked circularsubstrate arrangement according to an embodiment of the presentinvention.

[0133]FIG. 19B is a top view of a stacked circular substrate arrangementaccording to an embodiment of the present invention.

[0134]FIG. 20A is a schematic perspective view of a coated substratewith internal busbars formed on the surface according to an embodimentof the present invention.

[0135]FIG. 20B is a schematic perspective view of a coated substratewith two sets of internal busbars formed on the surface according to anembodiment of the present invention.

[0136]FIG. 21 is a schematic cross sectional view of a process to formembedded internal busbars on a substrate according to an embodiment ofthe present invention.

[0137]FIG. 22 is a schematic plan view of a device with internal busbarshaving different widths according to an embodiment of the presentinvention.

[0138]FIG. 23 is a schematic cross sectional side view of a device withinternal busbars having a transverse axis parallel to a sight line thatis at an angle to the surface normal according to an embodiment of thepresent invention.

[0139]FIG. 24 is a schematic cross sectional diagram of a deviceaccording to an embodiment of the present invention having internalbusbars that cause a property change when a signal is applied betweenthem, a different property change when a signal is applied along eachbusbar equally, and changes in both properties when a difference occursin the signals applied to each busbar according to an embodiment of thepresent invention.

[0140]FIG. 25A is a schematic plan view of a group of internal busbarsaddressable as a group according to an embodiment of the presentinvention.

[0141]FIG. 25B is a schematic plan view of a group of internal busbarsindividually addressable according to an embodiment of the presentinvention.

[0142]FIG. 26A is a schematic plan view of two groups of internalbusbars arranged at an angle to each other according to an embodiment ofthe present invention.

[0143]FIG. 26B is a schematic plan view of a group of internal busbarsarranged substantially parallel to each other according to an embodimentof the present invention.

[0144]FIG. 26C is a schematic plan view of a spiral internal busbaraccording to an embodiment of the present invention.

[0145]FIG. 27A is a schematic plan view of a group of internal busbarsconnected to the conductive layer by conductive posts according to anembodiment of the present invention.

[0146]FIG. 27B is a schematic side sectional view of a group of internalbusbars connected to the conductive layer by conductive posts accordingto an embodiment of the present invention.

[0147]FIG. 28 is a schematic perspective exploded view of a group ofinternal busbars connected to the conductive layer by conductive postsaccording to an embodiment of the present invention.

[0148]FIG. 29 is a schematic side sectional close up view of an internalbusbar connected to the conductive layer by a conductive post accordingto an embodiment of the present invention.

[0149]FIG. 30 is a graph of the transmissivity v. elapsed time for ECcells of different sizes without internal busbars or edge busbars.

[0150]FIG. 31A is a schematic plan view of a set of internal busbarsdisposed on a substrate according to an embodiment of the presentinvention.

[0151]FIG. 31B is a schematic sectional view of a set of internalbusbars disposed between two substrates according to an embodiment ofthe present invention.

[0152]FIG. 31C is a schematic sectional view of a set of internalbusbars disposed between two substrates according to an embodiment ofthe present invention.

[0153]FIG. 32A is a schematic sectional view of an electricallyreinforced edge busbar according to an embodiment of the presentinvention.

[0154]FIG. 32B is a schematic sectional view of an electricallyreinforced edge busbar according to an embodiment of the presentinvention.

[0155]FIG. 32C is a schematic sectional view of an electricallyreinforced edge busbar according to an embodiment of the presentinvention.

[0156]FIG. 32D is a schematic sectional view of an electricallyreinforced edge busbar according to an embodiment of the presentinvention.

[0157]FIG. 32E is a schematic sectional view of an electricallyreinforced edge busbar according to an embodiment of the presentinvention.

[0158]FIG. 33A is a plan view of an electrochromic cell according to anembodiment of the present invention.

[0159]FIG. 33B is a cross-sectional side view of an electrochromic cellaccording to an embodiment of the present invention.

[0160]FIG. 34A is a graph of the coloration kinetics of a 6″ by 3″ (15cm×7.5 cm) electrochromic window with internal busbars according to anembodiment of the present invention, and of a comparison electrochromicwindow without internal busbars.

[0161]FIG. 34B is a graph of the current/time behavior of a 6″ by 3″ (15cm×7.5 cm) electrochromic window with internal busbars according to anembodiment of the present invention, and of a comparison electrochromicwindow without internal busbars.

[0162]FIG. 35 is a graph of light transmission (T) and applied voltage(V) as a function of time (t) according to an embodiment of the presentinvention.

[0163]FIG. 36A is a circuit diagram of an embodiment of the presentinvention that includes a thermistor.

[0164]FIG. 36B is a circuit diagram of an embodiment of the presentinvention that includes a micro-controller.

[0165]FIG. 37A is a circuit diagram of a switching regulator circuitaccording to an embodiment of the present invention.

[0166]FIG. 37B is a circuit diagram of a switching regulator circuitaccording to an embodiment of the present invention.

[0167]FIG. 37C is a circuit diagram of a switching regulator circuitaccording to an embodiment of the present invention yielding a very lowquiescent current.

[0168]FIG. 38A is a circuit diagram of a switching regulator circuitaccording to an embodiment of the present invention having a resistorplaced in series with the power supply output and EC cell.

[0169]FIG. 38B describes the various shapes that the voltage vs. timecurve can follow depending on the parameters of the control circuit ofthe present invention that controls an EC cell and compared to the priorart continuous step shape and the prior art linear ramp shape.

[0170]FIG. 38C describes the various shapes that the voltage vs. timecurves can follow depending on the circuit resistance parameters.

[0171]FIG. 39 is a circuit diagram illustrating the incorporation of anop amp and thermistor in a circuit for regulating the voltage suppliedto an EC cell.

[0172]FIG. 40 is a circuit diagram illustrating the use of a thermistorin a circuit to vary the output voltage with temperature.

[0173]FIG. 41 is a circuit diagram illustrating the use of a thermistorin a comparator circuit.

[0174]FIG. 42 is a circuit diagram illustrating the use of a thermistorin a comparator circuit.

[0175]FIG. 43 is a circuit diagram illustrating the use of an adjustablevoltage power supply with an EC device.

[0176]FIG. 44 is a circuit diagram illustrating the use of a sensingresistor in series with the power output to limit the maximum currentflowing in the circuit.

[0177]FIG. 45 illustrates an electric circuit attached to an EC cellhaving switches that may be used to determine t₁ or t₁ by mesuring thevoltage at the EC cell V_(cell) and comparing the value with V_(c) orV_(B.)

DETAILED DESCRIPTION OF THE INVENTION

[0178] Edge Busbars

[0179] In the present invention, a conductive path is formed from theelectrodes to the edges of the substrate. Preferably, this path isextended on to the back of the substrate as shown in FIGS. 7A and 7B(the details of other coatings employed in the device have beenomitted). Two substrates 701 and 702 are shown attached to each other atclose proximity by cell adhesive 703. On the edge of the device,preferably including on the back, highly conductive paths are employedto lower the busbar resistance. FIG. 7A shows an edge busbar 704 of thepresent invention which wraps around the edge of the substrate toprovide highly conductive paths on three sides of the edge. FIG. 7Bshows a conductive path 706 of the present invention to which isattached a highly conductive perimeter portion 705.

[0180] The conductive path 706 from the front of the substrates to theback could be the continuation of the same material which is used forthe transparent conductor on the substrate, such as indium tin oxide, orcan be fabricated from a different material. Once the conductive path isformed on the back of the substrates, the geometrical limitations on thethickness and the width of the busbar conductor are relievedsubstantially because the perimeter portion can cover a larger areawithout concerns about thickness. The busbar of the present inventionincludes the conductive path and the perimeter portion.

[0181] Conductive path 706 forms an electrical connection from the frontto the back. Therefore, the paths can be called connector portions.These electrical connector portions can be made using conductiveadhesives, silver frits (e.g., available from Dupont ElectronicMaterials, Research Triangle Park, N.C. or FX 33-246 available fromFerro Inc. of Santa Barbra, Calif.), solder materials, physical vapordeposition, chemical vapor deposition, electroless deposition of metals,metallo-organics (e.g., available from Engelhard Electronic Materials,N.J.) and conductive tapes. The conductivity of these connector portionsneed not be as high as the perimeter portions that connect to theseconnector portions because the connector portions only have to carry thecurrent over a short distance, hence their actual effective resistanceis low.

[0182] These connector portions could be continuous, thereby mergingwith the perimeter portion, or in strips. Either connector portionconfiguration, continuous or strips, encompasses a substantial portionof the device perimeter. FIG. 8A shows two substrates 801 and 802,separated for clarity. Substrate 802 is shown with a continuousconductive path 803. FIG. 8B shows substrate 802, continuous conductivepath 803, and an adhesive 804. FIG. 8C shows a substrate 802′, stripconductive paths 803′, and adhesive 804. In FIG. 8C, perimeter portion805 connects strip conductive paths 803′. Perimeter portion 805 extendsto a back perimeter region (not shown).

[0183] According to the present invention, referring to FIGS. 8B and 8C,it is not necessary to have a width of the substrate exposed between thesealant or adhesive 804 and the connector portion or conductive paths803 and 803′. Depending on the nature of the sealant and connectorportion and their bonding characteristics, a partial or a completeoverlap may exist. If the connector portion of the present invention isused in the strip form as shown in FIG. 8C, the connector portion stripson the bottom and on the top substrates may be offset from each other,may be stacked on top of each other, or may have no particularly setgeometric relationship.

[0184] In a preferred configuration where the connector portion stripsare offset, the thicknesses may be increased almost to the point wherethey occupy the entire gap between the substrates without shorting. Suchconnector portion strips are offset effective to allow an insulatingdistance between a particular connector portion strip and anyneighboring connector portion strips connected to an opposite substrate,as well as between the particular connector portion strip and theopposite substrate. The insulating distance can include insulatingmaterial. The insulating material can also be preformed on theconductive strips. In a particularly preferred configuration, theconnector portion strips from one substrate are in an alternatingrelationship to the connector portion strips of the other substrate.

[0185] The perimeter portion materials could be selected from the samelist of materials as the connector portions. However, to enhance theirconductance, materials with high conductivity could be selected and/orthe geometry (i.e., increased thickness, width, perimeter portions etc.)may be different from the connector portions.

[0186] Thick metallic strips and wires may also be used as perimeterportions. The conductive path of the connector portions of the presentinvention overcomes the prior art's dependence on the busbars' specificconductivity because the present invention provides a broad area ofconductance to which the connector portion is attached.

[0187] The devices are preferably assembled (e.g., by bonding togethertwo substrates) after the connector portion strips or front to backconnections are attached to each of the substrates. If counterelectrodecoatings are required in the EC device, such strip connector portionscan be formed or positioned before or after these coatings aredeposited. Further, the part of the connector portion strips on the backof the substrates can be joined or reinforced (such as with conductivecopper tapes) with highly conducting medium either before or after thedevice assembly. The adhesive in the copper tapes may be pressuresensitive adhesive (PSA), or may be curable later into a thermosettingmaterial by the application of pressure, heat, radiation, moisture, ormore than one of these methods.

[0188] As described above, and further below, the edge busbars of thisinvention can be augmented (“reinforced”) in conductivity. That is, theelectrical conductivity is augmented or reinforced in order to increasethe busbar electrical conductivity, by such methods as (i) by wrapping acontinuous connector from the front to the back of the substrate, thusproviding a wider conductor resulting in higher electrical conductivity,(ii) by attaching the connector to a conductive wire, foil, or tapepositioned on the back of the substrate so that the connector'sconductivity can be augmented by the conductance of the wire, foil,solder, frit, or tape, and (iii) attaching a wire or conductor on theedge of the substrate to electrically contact the connector in order toaugment the conductance of the connector.

[0189] A preferred method to form the edge busbar is to use a conductivetape with a conductive adhesive layer that conducts through the adhesivelayer thickness. FIG. 9B shows a conductive tape 909 having a conductor911, a conducting adhesive layer 912 and an optional insulating layer910. A continuous strip of such a tape is shown in FIG. 9C. Tape 909includes the continuous conductor or perimeter portion 913, and fingersor connector portions 914 that will form the contact with thetransparent conductor on the front side of the substrate. The frontside, as defined previously, refers to the substrate side that faces theother substrate of an EC device, while the back of a substrate refers tothe side, opposite to the front side, that faces away or is farther awayfrom the other substrate. Tape 909 connects the front of the substrate(facing inward) by way of connector portions 914 to perimeter portion913 at the back of the substrate. An edge portion 915 of connectorportion 914 lies on the edge of the substrate.

[0190] As shown in FIG. 9C, perimeter portion 913 and strip connectorportion 914 could be integrally connected, i.e., one piece of tape ofthe perimeter portion is preferably aligned with the bottom edge of thesubstrate, or is on the backside of the substrate. The flat side isfolded and adhered to the substrate back. For a rectangular device withsharp corners, the tape in the corner could be folded over the back sideto form a crease without effecting the connector portions at the frontside. Since there is effectively no limitation on the gap or tapethickness on the back side (or the outside) of the device, the procedureof the present invention can be used without affecting the separationdistance of the substrates. Instead of a crease on the back side, thetape can be cut and the tape strips running at an angle to each othercan be folded on top of each other on the corners. The corners may alsobe bridged by a piece of another tape, wire, solder, etc., to keeppreferably one continuous electrical path forming a perimeter portionfor each substrate. The tape or the strip on the back can be made moreconductive by reinforcing the tape with a more conductive medium, e.g.,more tape, wire, metallic strip, etc. Accordingly, the perimeter portioncan be multilayered or made from a number of components.

[0191] In this description, the use of the above shape of the tape (i.e.tape with connector portions or fingers extending from a continuousperimeter portion) avoids any kinds of creases or kinks on the frontsurface. Such kinks can develop as the tape traverses over the cornersof the substrate. It is readily understood that as an edge bends to forma curve or to form a corner, an inner path which is a certain distancefrom the outer edge will trace a different distance from the outer edge.In the case of a convex curve, the inner path will be shorter.Accordingly, a non-stretching material will tend to crease or kink totry to accommodate the excess material on such an inner path. Therecesses between each connector portion prevents accumulation of excessmaterial on the front side between the substrates.

[0192] The above description shows a tape that is easily andadvantageously used for applications where a pair of edge busbars can beplaced correspondingly opposite each other on two substrates withoutphysical interference or electrical shorting because of the innovativegeometry of the edge busbar pairs of the present invention. Suchgeometry innovatively allows the pair of edge busbars to nest togetherin an alternating relation. Such geometry further innovatively allowseach of the pair of edge busbars to be thicker than half the gapseparating the substrates on which they cover, thereby increasing theedge busbar conductivity without shorting to each other. Such geometryalso allows edge busbars to wrap around corners without interferingbusbar material in between the substrate separation gap.

[0193] For those EC panels that are rectangular in shape, it isparticularly at the corners that certain configurations of the presentinvention are important. It is important to ensure that no fingers arelocated on those areas of the tape which bend around the sharp corners.Furthermore, the fingers are spaced such that they do not overlap eachother over the conductive substrates. Any kinks, overlaps, or creases onthe front (conductive) side can interfere with the predetermined gapbetween the two substrates and, depending on the materials employed,could also lead to electrical shorting between the two substrates.

[0194] The tape shown in FIG. 9C can optionally have an additional rowof strip connector portions 914 (not shown) on the side of perimeterportion 913 opposite the side with the row of strip connector portions914 shown. In this optional configuration, perimeter portion 913 isaffixed to the edge of the substrate and the each opposite rows of stripconnector portions 914 are affixed to respective opposite surfaces ofthe substrate.

[0195] Besides for substrates with sharp corners, the geometry of thetapes described above can be similarly employed for substrates withcircular, elliptical, or any other regular or irregular shapes. Forshapes that have a gradual change, such as a circle, the width of thestrip connector fingers and the spacing between them should be such sothat no noticeable kink is introduced on the front side of the substratefor the reasons described above.

[0196] The electrical connections to the device are made from theperimeter portion on the back of the substrate by using more conductivetape, solder, adhesive, wires, etc., or preferably the tape describedabove may be provided in a pre-cut size and shape that has a connectoror a connector attachment already assembled.

[0197] As shown in FIG. 9A, it is preferable for connector portion 914of each tape 909 to be in an alternating relationship with the connectorportions 914 of the other tape 909 to minimize the chances of shortingor of overlapping of fingers. As shown in FIG. 9D, a corner of substrate901 and a corner of substrate 902 meet without any connector portions914 at the corners. The connector portions 914 remain in an alternatingrelationship to prevent any overlap of tape conductive material

[0198] As shown in FIG. 9B, tape 909 employed for this purpose can becoated or laminated with a nonconductive material insulating layer 910on the side that is non-adhering. This will reduce the chances forshorting of the two substrates should the fingers inadvertently overlapor if there is a malfunction, for example, when one of the strip fingerslifts off the surface.

[0199] In another method, highly conductive busbars are made by wrappingthe connector from the substrate front to the substrate edges and thenreinforcing the edge portion with a highly conductive material. This isshown in FIGS. 32A and 32D. The connectors are shown as 3205 and 3205″and the reinforcements as 3203 and 3203′″ forming the busbars 3202 and3202′″. The reinforcement can be any convenient shape such as acylindrical wire, as shown for example. Another shape is a flattenedwire. In this example the conductor is shown significantly thicker atthe edges than its thickness on the front of the substrate. In FIG. 32D,the reinforcement is located in a precut groove on the edges of thesubstrate.

[0200]FIG. 32E shows highly conductive reinforced busbars having thereinforcement in a groove with the conductive connector wrapping fromthe front of the substrate around the edge to the opposite side of thesubstrate.

[0201] The busbars can be made by any convenient method such as, forexample, by feeding the reinforcing wire and solder (as connector) sothat both can be put in place simultaneously. Another method could bewhere the wire is pre-attached, e.g., by wrapping and then mechanicallytightening around the perimeter of the substrate. The solder is thendeposited on the front and the edge thus electrically attaching thereinforcement with the connector. In this method it may be advantageousto have a precut groove on the perimeter edge of the substrate in whichthe wire can be placed, as shown in FIG. 32D.

[0202] The arrangement shown in FIG. 32A can be modified as shown inFIGS. 32B and 32C where the connector wraps around from the front to theback. Similarly, the conductor shown in FIG. 32D can be extended byhaving a wrap around connector (as shown in FIG. 32E). Further, the wiremay be placed in a groove on the edge (as shown in FIG. 32D) or in agroove made in the back of the substrate close to the perimeter edge(not shown).

[0203] The connector may be deposited by using a soldering iron, withits tip shaped so that the solder can be melted and simultaneouslydeposited on two adjacent surfaces (as shown in FIG. 32A) or on threeadjacent edges (as shown in FIG. 32B). Instead of using a solder, aconducting adhesive may also be applied. The solder or adhesive may beapplied from a bath of molten solder or uncured liquid adhesive bydipping the substrate edge in the bath and then moving the part (e.g.,rotationally) effective to cover a substantial perimeter of thesubstrate.

[0204] To improve the reliability of the connections, it is preferred toseal the device using a non-conducting adhesive. As shown in FIG. 10, itmay even be desirable to allow the edge sealant adhesive to fill in theremaining gap between the substrates and preferably extend to thesubstrates edges for improved reliability. Substrates 1001 and 1002 areseparated and attached to each other by cell adhesive 1003. Edge busbars1005 including conductive paths that wrap around to the fronts ofsubstrates 1001 and 1002 have an edge sealant 1004 filling therespective gaps between each opposite pairs of edge busbars. Anyconvenient non-conducting material can be used such as, for example, acurable formulation such as a caulking, a heat or radiation curablematerial, or a hot melt adhesive that cures later, or a non-curableformulation such as a hot-melt adhesive. Some examples of materials usedin sealants are silicones, polysulfides, butyls, urethanes, epoxies,vinyls, polyolefins, polyamides and acrylics, etc. Hot melt urethanesthat cure later due to the diffusion of moisture may be preferred as asealant because devices so made could be handled soon after fabricationand a non-flowable, non-sagging bond is obtained after curing. One maypreferably employ the cell adhesive 1003 to be the same as edge sealant1004. This adhesive may have spacers so that the cell spacing isgoverned by the size of these spaces and the thickness of edge busbars1005. This avoids electrical shorts between the two substrates, due tobusbar peel, moisture condensation or conductive impurity.

[0205] Although the present invention has been discussed in terms ofelectrochromic devices, it can also be useful in photochromic devices(U.S. Pat. No. 5,604,626, incorporated herein by reference), liquidcrystal based devices as described in Motogomery, G. P., in Large-AreaChromogenics: Materials and Devices for Transmittance Control, SPIEOptical Engineering Press, Bellingham, Wash., 1990, p. 577, suspendedparticle devices (Research Frontiers Inc., Woodbury, N.Y.) and otherdevices.

[0206] Highly conductive busbars may be deposited on single substratedevices in a number of ways to achieve substantial perimeter contact. Inthe prior art, for example in U.S. Pat. No. 5,187,607, incorporatedherein by reference, the busbars for an EC device do not cover asubstantial perimeter of the device. As shown in FIG. 12 (taken fromU.S. Pat. No. 5,187,607) a busbar is formed on the edges of thesubstrate. The first transparent coating layer (bottom conductor) isdeposited so that it touches both the busbars, but it is not continuous.This coating is either etched or deposited in such a way (e.g., bymasking) that there is no electrical continuity between the two busbars.The coatings which comprise the EC stack are substantially deposited onone of these sections. However, the top conductor is deposited in such away that it touches the second part of the bottom conductor and iselectrically insulated from the first part of the bottom conductor bythe EC stack. Thus, in this design none of the two busbars occupies asubstantial perimeter of the device. Instead, the busbars run along thetwo edges similar to the prior art discussed previously.

[0207] As shown in FIGS. 11A, and 11B, the use of busbars according tothe present invention which are deposited on a substantial perimeter ofan electric cell can be effectively employed for those devices that usethin coatings on one substrate. A substrate 1101 has a transparentelectrode 1102 on its front surface. An EC stack 1104 is on thetransparent conductor 1102. A bottom busbar 1103 is formed on theperimeter of the transparent conductor 1102 while a top busbar 1105 isformed on the perimeter of the top of the EC stack. Electric leads areconnected to each busbar.

[0208] As shown in FIG. 13, a bottom electrode 1402 is formed onsubstrate 1405 in a pattern with recesses 1301 at the edges of bottomelectrode 1402. Bottom electrode 1402 can be formed by any convenientmethod such as, for example, by depositing the bottom electrode (e.g.made from ITO, doped tin oxide, doped zinc oxide, etc.) over anappropriate mask, or by etching through an appropriate mask afterdeposition. Preferably, the sheet resistance of the transparentconductors is less than about 30 Ω/▪, more preferably less than about 15Ω/▪, and most preferably less than about 10 Ω/▪.

[0209] The EC stack is then deposited along with the top electrode onlyonto the device area, and recesses 1301 in the electrode border area.Optionally, one can deposit the EC stack over the device area and onlythe top electrode layer would extend into recesses 1301 of the electrodeborder. It is important to keep the top electrode layer and the bottomelectrode layer from shorting, thus it is desirable that the topelectrode be deposited in such a way that it covers only a portion ofrecesses 1301 in the border region to avoid shorting. Optionally, aninsulating layer can be deposited.

[0210] As shown in FIGS. 14, 15A, and 15B, one embodiment includesforming an EC stack 1406 on bottom electrode 1402. A top electrode 1401is formed on EC stack 1406. An edge busbar 1404 connects to topelectrode 1401, while an edge busbar 1403 connects to bottom electrode1402. Edge busbar 1404 comprises a perimeter portion 1404C and aconnector portion 1404D. Connector portion 1404D includes a contactingportion 1404A and an edge portion 1404B. Contacting portion 1404Aelectrically contacts a surface of top electrode 1401. Edge busbar 1403comprises a perimeter portion 1403C and a connector portion 1403D.Connector portion 1403D includes a contacting portion 1403A and an edgeportion 1403B. Contacting portion 1403A electrically contacts a surfaceof bottom electrode 1402. Connector portion 1404D and 1403D are inalternating relationship on each side of EC device 1444.

[0211] One method to form the continuous busbar on this device is toutilize a tape as shown in FIGS. 9B and 9C. As described earlier, thefirst tape is placed around the periphery of the device with its fingerstouching the bottom electrode in the connector border area. Thecontinuous body of the tape is folded and adhered to the back of thesubstrate. The fingers of the tapes form the connector portions 1403Dand 1404D. The fingers of the second tape are then adhered on the topelectrode (in the connector border area) and folded and adhered to theback of the substrate.

[0212] The tapes, after assembly, appear as shown in FIG. 15A and 15B ina cross-section view (two sections shown from FIG. 14). One of the tapesis wider, in order to protrude out. Perimeter portion 1403C extendsbeyond perimeter portion 1404C to expose surface 1403E. This allowsconnection to be made to both edge busbars 1403 and 1404 directly to anyconvenient point or points on perimeter portion 1404C and to anyconvenient point or points on exposed perimeter portion 1403E.

[0213] Referring to FIG. 15C, the connection can be made by removing theinsulating layer locally, or the tape may come with a connector-adapterand/or connector pre-attached as discussed earlier. Connections 1408Aand 1408B are shown connecting to perimeter portions 1403C and 1404C,respectively while being insulated from perimeter portions 1404C and1403C, respectively. Connections 1408A and 1408B can be, for example, aconductive wire or tape connected to an exterior signal connector.Connections 1408A and 1408B can be attached at only one corner (asmaller portion of the device perimeter), or at a longer portion of thedevice perimeter such as, for example, a substantial perimeter.

[0214] In all cases, one must be careful that the two busbars 1403 and1404 do not electrically short in the regions 1410 where an edge ofperimeter portion 1403C meets edge portion 1404B at the edge ofsubstrate 1405. Shorting can be avoided by ensuring that the insulatorlayer of the tape extends out and covers the edges of the conductor.Alternatively, after adhering the first tape, these edges can be treatedwith an insulating material (tape, adhesive, coating) before the secondtape is applied.

[0215] Once all the edge busbars are in place, the edges of the ECdevice 1444 can be encapsulated, for example, by injection molding(e.g., using thermoplastic elastomers or plasticized polyvinyl chloride)or reaction injection mold (e.g., using polyurethane) with a resin thatcan be solidified to ensure the reliability of the connections. It mayeven be desirable to cover the entire device with another substrate(preferably a glass or a plastic sheet) for mechanical and environmentalprotection before edge encapsulation. This cover substrate may alsoincorporate UV blocking characteristics. The edge encapsulation may beachieved such that a connector plug (which is internally connected tothe busbars) is molded therein which can be easily disconnected from thepower supply. This will allow EC panels to be quickly serviced andreplaced in the field.

[0216] As shown in FIGS. 16A and 16B, busbars 1602 may be embedded inthe edge of a substrate 1601 or busbars 1603 may be embedded in the edgeregions of substrate 1601. The appropriate region of the substrate isetched, ablated, or otherwise conveniently removed to form a recess. Ahighly conductive material (e.g., a metal) is deposited into the recessregion. Planarization, to bring the substrate surface and the busbarssubstantially to a plane, may be necessary prior to the deposition of anadditional layer or layers. Such embedded busbars 1602 and 1603 canserve as perimeter portions with connector portions formed (not shown)by any convenient method such as, for example, wrapping tape around theedge to contact the back surface and the embedded busbar, depositingconductive material such as a frit or a coating around the edge from theembedded busbar to the back surface, or attaching a multitude ofpreformed conductive channels to the edge to contact the back surfaceand the embedded busbar.

[0217] As described previously, the edge busbar of the present inventionprovides sufficient conductivity such that a negligible voltage drop(preferably less than one tenth of the applied voltage) occurs in theedge busbar. The conductivity can be optionally reinforced by theaddition of a supplemental conductor portion as part of the edge busbarof the present invention, as shown in FIGS. 32A, 32B, and 32C. In apreferred embodiment, an ultrasonic solder dispenses an appropriatesoldering material on the edge of the substrate. A highly conductivemedium (e.g. a wire, conductive tape or foil, etc.) is attached toreinforce the overall conductance around a substantial perimeter of thesubstrate. It is preferable that both the solder and Whe wire or stripare dispensed simultaneously to form the edge busbar and thereinforcement at the same time.

[0218] The reinforcement bar can also be in the form of a closed loopwith a perimeter slightly smaller than that of the substrate. In thiscase, after applying the edge busbar, the reinforcement is expanded byheating and positioned around the edge making contact with the busbar.Of necessary, it can be soldered to further improve electrical contact.This method is particularly appropriate in the case of cells havingcircular or oval substrates where the reinforcement can be made in theform of a ring and contracted, by cooling, uniformly around thesubstrate. Finally, a lead can be soldered to the reinforcement.

[0219] Referring to FIG. 32A, an edge busbar 3202 is formed on aperipheral surface and a substantial perimeter edge of a substrate 3201.Edge busbar 3202 includes a reinforcement portion 3203 which can be anyconvenient conductor such as, for example, wire, foil, or bead ofsolder. Reinforcement portion 3203 is shown as a circularcross-sectional wire attached to the side of the edge portion 3205 ofedge busbar 3202. A connection 3204 provides an external electrical leadto edge busbar 3202.

[0220] Referring to FIG. 32B, an edge busbar 3202′ is formed on opposingperipheral surfaces and a substantial perimeter edge of a substrate3201. Edge busbar 3202′ includes a reinforcement portion 3203′ which isshown as a circular cross-sectional wire attached to the side of theedge portion 3205′ of edge busbar 3202′. A connection 3204′ provides anexternal electrical lead to edge busbar 3202′.

[0221] Referring to FIG. 32C, an edge busbar 320211 is formed onopposing peripheral surfaces and a substantial perimeter edge of asubstrate 3201. Edge busbar 3202″ includes a reinforcement portion 3203″which is shown as a circular cross-sectional wire attached to oneperipheral edge portion 3206 of edge busbar 3202″. A connection 3204″provides an external electrical lead to edge busbar 3202″.

[0222] Referring to FIG. 33A, a substrate 3301 is shown having a solderedge busbar 3302. Solder edge busbar 3302 is in electrical contact withone segment of a silver frit layer 3303. Another segment of silver fritlayer 3303 forms an internal busbar 3304. Internal busbar 3304 isinterior to the perimeter formed by a main epoxy seal 3305.

[0223] Referring to FIG. 33B, two substrates 3301′ and 3301″, each has asolder edge busbar 3302′ and 3302″ respectively. Each solder edge busbar3302′ and 3302″ are in contact with segments of silver frit layers 3303′and 3303″. A common epoxy seal 3305′ bounds internal busbars 3304′ and330411 which are segments of silver frit layers 3303′ and 3303″respectively.

[0224] The Examples which follow are intended as an illustration ofcertain preferred embodiments of the invention, and no limitation of theinvention is implied.

EXAMPLES Example 1 and Comparative Examples 1C and 2C

[0225] EC devices were made having two substrates, one employing a onehalf wave ITO (about 12 ohms/square) on glass substrate (from DonnellyApplied Films, Boulder, CO) and the other being a TEC 15 glass (fromLibby Owens Ford (LOF), Toledo, Ohio). The nominal size of these was 6inch by 6 inch (15 cm×15 cm). The gap between the substrates was 210micrometers. Busbars were formed using a copper tape with conductiveadhesive. Three different configurations were made: (i) ComparativeExample 1C was made in a configuration as shown in FIG. 2, where theedge busbar was on one edge of each substrate, (ii) Comparative Example2C was made in a configuration as shown in FIG. 4, where the edgebusbars are on the two edges of each substrate, and (iii) Example 1 wasmade in a configuration as shown in FIG. 7A and constructed by a methodas shown in FIGS. 17A and 17B, where the edge busbars are on four edgesof each substrate. Copper tape (with conductive pressure sensitiveadhesive) was used to form the busbars. The thickness of the copper tapewas 50 micrometers and a width of 3 mm.

[0226] To form the busbar on all four edges, as shown in FIGS. 17A and17B, four strips of copper tape 1701 were attached to substrate 1702 andthen folded on the back of the substrate. Care was taken that thesestrips were close but not overlapping. On only one of the substrates,the copper tape was covered with a 50 micrometer thick polyimide tape,the latter was wider than the copper tape by about {fraction (1/32)} ofan inch (0.079 cm). This was done to prevent shorting of the twosubstrates if the copper tape peeled accidentally and touched the othersubstrate. Optionally, tabs 1703 can be formed by extending one portionof copper tape 1701. The two substrates were then adhered to each otherin a configuration shown in FIG. 7A. The total gap between the twosubstrates was 210 micrometers (controlled by the adhesive) and thetotal thickness of the tape was 150 micrometers.

[0227] The assembled cells were powered by connecting power to thebusbars. In the case of Example 1, power was connected to one of thecopper tabs 1703 sticking out from each of the substrates. In thisexample the tabs were not joined by a wire or a tape on the back. Sincethe distance between the adjacent copper strips was small, the potentialdrop in the intervening ITO was negligible for this device. Thus, thebusbars of Example 1 effectively formed a continuous electricalconductor around each substrate perimeter. The continuous electricalconductor of Example 1 included the connector portions being effectivelyelectrically continuous as well as the perimeter portions beingeffectively electrically continuous.

[0228]FIG. 18 shows the kinetic traces of each of the three devices whenthey were colored and bleached by applying identical step potentials.Example 1, the cell with busbar on all four sides colors, was thefastest to color and colored the deepest (during the time shown in thegraph), while Comparative Example 1C, the one with busbar only on oneedge, was the slowest to color and also colored the least deep of thethree devices.

Example 2

[0229] An EC device 1910 was made using two TEC 15 transparentconductive substrates as shown in FIGS. 19A and 19B. Example 2 was acircular EC device 1910 with a substrate 1902 being 13 inches (33.02 cm)in diameter and a second smaller substrate 1901 being 12 inch (30 cm) indiameter. Before EC device 1910 was assembled, a busbar 1904 on thesmaller substrate 1901 was formed by screening on a silver frit fromDupont Electronic Materials, Wilmington, Del. (frit Type 7713). The fritforming was deposited in a perimeter ring geometry to form busbar 1904,with the outer dimensions of the ring being substantially the same asthat of substrate 1901. The width of the ring was 2 mm and the thicknesswas 5.5 micrometers. In one part of the busbar 1904 ring the silver fritwas painted on the edge (while keeping it connected to the ring) andextended on to the back of the substrate to form a conductive path 1908of busbar 1904 which is conductive from the front to the back. Anelectrical conducting wire 1906 is connected to conductive path 1908 onthe back.

[0230] Substrate 1901 was heated to 575° C. for 6 minutes to consolidateand cure the frit. The busbar 1905 on the larger substrate 1902 wasformed by attaching a copper beryllium spring clip 1905 around thecircumference. Spring clip 1905 comprises a continuous perimeter portion1911 which extends circumferentially around the edge of substrate 1902,and finger connector portions 1912 which extends radially fromcontinuous perimeter portion 1911 to substrate 1902. A conducting wire1907 was soldered to clip 1905 to power substrate 1902. EC cell 1910 wasassembled by gluing the two substrates together with adhesive 1903, asshown in FIGS. 19A and 19B. The smaller substrate 1901 was keptconcentric with the larger substrate 1902.

[0231] Internal Busbars

[0232] To produce the desired improvements in EC device behavior, it isnecessary to reduce appreciably the effective resistance of thetransparent electronic conductors (TC) in the devices or to otherwisetransport charge more efficiently laterally across the device. Incontrast to the case of a TC, when the transparency of a particularelectronically conducting electrode (ECE) is not important, the ECE cangenerally be made thick enough in the prior art so that its resistancedoes not adversely affect the device behavior. For example, for a priorart mirror device with an Aluminum (Al) ECE and an ITO ECE, the Al layercan be deposited sufficiently thick. The result, however, is that theeffective resistance of the ITO (the transparent electronic conductor orTC) usually is the primary limiting factor which must be overcome toimprove the device behavior.

[0233] In reducing the effective resistance of a TC, it is crucial toensure that the means employed does not adversely affect othercomponents of the device operation. This is especially problematic whenthe TC acts as a substrate for an active EC layer or layers (such as fordevices which contain EC tungsten oxide deposited on ITO-coated glasssubstrates). In addition, one must ensure that the means employed do nottoo strongly diminish the transmissivity or apparent transmissivity ofthe TC or otherwise adversely affect the cosmetics of the device. Forexample, the resistance of the TC may be decreased appreciably byincreasing its thickness, but increased thickness generally has astrongly negative impact on TC transmissivity characteristics and cost.

[0234] Means for Decreasing the Effective Resistance of The TC's

[0235] A desirable means of imparting a relatively high effectiveconductivity to a TC comprises depositing a pattern of a highlyconductive material over, under, or within it (or some combination).Commercially available TC's such as half-wave ITO or doped tin oxide(DTO) can be used and modified by adding internal busbars according tothe present invention. As shown in FIGS. 20A and 20B, e.g., the patterncan be formed as lines across the substrate. These lines may or may notintersect. The lines or patterns may be referred to as internal busbars(IB's). FIG. 20A shows a substrate 2001 made of, for example, glass,coated with a transparent conductive coating 2002. Internal busbars 2003are formed on conductive coating 2002, FIG. 20B shows additionalinternal busbars 2004 transverse to internal busbars 2003.

[0236] It is important to ensure that the materials used for theinternal busbars (IB) of the present invention do not react with thecell components. That is, the internal busbars should be chemically andelectrochemically isolated from the reactive layers of the cell.Reactive layers are the electrolyte, the ion insertion electrodes, andthe electrochromic layers. In these layers, chemical and physicalreactions take place when the cell is colored or bleached.

[0237] The chemical and electrochemical isolation can be by anyconvenient means such as, for example, by interposing a barrier layerbetween the IB and the reactive layer. The property of being notionically conductive is a requirement of the optical passivation layerso that, when a voltage is applied to the finished cell for coloring orbleaching, no ion transport takes place from any of the cell componentsto the internal busbars and vice versa.

[0238] As described below and in the figures, the isolated IB's of thisinvention are connected to the conductive layers by connecting portionsthat are electrically conductive. Accordingly, the IB's of thisinvention can provide substantial improvement of the electricalproperties of the conductive layer while not being in contact with thelayer.

[0239] A calculation of the effective sheet resistance corresponding toa pattern consisting of parallel lines on a transparent conductor wasperformed. The physical dimensions of these internal busbars (e.g.,their thickness (or height), width, length, resistivity) along with theunderlying transparent conductor characteristics, determine the overalleffective sheet resistance. Tables 1A, 1B, and 1C below show thecalculated effective sheet resistance of the substrates for variousvalues of the relevant parameters. The calculations were made for 5 cm×5cm square substrates traversed by five (n=5, or “N₅”) parallel internalbusbars, each of width w_(s) and height h_(s). For these calculations,the strips were assumed to be composed of Pt-metal (σ=0.96×10⁵(Ωcm)⁻¹).The effective sheet resistance was taken as the resistance that would bemeasured between an electrode connected on one full side of the squareand another connected to the opposite full side. It should be noted thatthe calculations can be repeated for a grid pattern which may consist ofcurved lines or non-uniformly dimensioned (e.g., in width and thickness)conductive line patterns. TABLE 1A h_(s)\w_(s) w_(s) h_(s) 0.01 mm 0.05mm 0.1 mm 0.15 mm 100 nm 13.29 13.448 13.396 13.344 1 μm 12.526 9.7217.595 6.232 2 μm 11.683 7.595 5.283 4.051 3 μm 10.946 6.232 4.051 3.0014 μm 10.297 5.283 3.284 2.383 0.1 mm 1.538 0.339 0.171 0.115

[0240] Table 1A. Calculated effective sheet resistances Ω/▪ for a systemcomprising 3 strips, where each strip possesses the dimensions (h_(s),w_(s)) given in the Table. TABLE 1B h_(s)\N_(s) N_(s) h_(s) 1 2 3 4 5100 nm 13.448 13.396 13.344 13.293 13.243  1 μm 9.721 7.595 6.232 5.2834.586  2 μm 7.595 5.283 4.051 3.284 2.762  3 μm 6.232 4.051 3.001 2.3831.976  4 μm 5.283 3.284 2.383 1.87 1.538  0.1 mm 0.339 0.171 0.115 0.0860.069

[0241] Table 1B. Calculated effective sheet resistances Ω/▪ for a systemcomprising Ns strips, where each strip possesses a width of 0.15 mm anda height, h_(s), as indicated in the Table. TABLE 10 w_(s)\N_(s) N_(s)w_(s) 1 2 3 4 5 0.01 mm 12.232 11.181 10.297 9.543 8.891 0.05 mm 8.8916.628 5.283 4.392 3.758  0.1 mm 6.628 4.392 3.284 2.623 2.183 0.15 mm5.283 3.284 2.383 1.87 1.538

[0242] Table 1C. Calculated effective sheet resistances Ω/▪ for a systemcomprising N_(s) strips, where each strip possesses a height of 4 μm anda width, w_(s), as indicated in the Table.

[0243] The effect of size on the conductance of a 15 Ω/▪ (TEC 15)substrate with internal busbars is shown in Tables 2A and 2B below.

[0244] Two different systems are considered:

[0245] System A: IB's comprise Pt-strips (σ=0.96×10⁵ (Ω·cm)³¹ ¹), each0.15 mm wide and 41 μm high; and

[0246] System B: IB's comprise strips of DuPont 7713 Frit with a sheetresistance of R_(s)=3 m Ω/▪ at 25 μm thickness. Each strip is 1.5 mmwide and 25 μm high.

[0247] The number, N_(s), of IB's is such that there is a fixed spacingof 1 cm between busbars. Edge busbars are not represented in thecalculations (so, e.g., for a L cm×L cm system, there are (L−l) IB's).In all cases, the underlying conducting sheet possesses a sheetresistance of 15 Ω/▪. TABLE 2A Calculated effective sheet resistance forSystems A and B R_(Sheet) for R_(sheet) for Substrate Area System “A”System “B” 5 cm × 5 cm 1.90 Ω/▪ 0.0250 Ω/▪ 10 cm × 10 cm 1.71 Ω/▪ 0.0222Ω/▪ 30 cm × 30 cm 1.60 Ω/▪ 0.0207 Ω/▪ 100 cm × 100 cm 1.57 Ω/▪ 0.0202Ω/▪

[0248] The effective sheet resistance is useful for comparing substratesof comparable size. However, an effective resistance (R), defined as theeffective sheet resistance multiplied by the area of the substrate (thuspossessing units of Ω·cm²/▪), is more useful for comparing substrates ofdifferent sizes. Table 2B comprises the data for the effectiveresistance (R), for each sheet, as a function of substrate size. TABLE2B Calculated effective resistances for Systems A and B. EffectiveEffective Resistance Resistance for System for System Substrate Area “A”“B” 5 cm × 5 cm 47.4 Ω · cm²/▪ 0.624 Ω · cm²/▪ 10 cm × 10 cm 171 Ω ·cm²/▪ 2.22 Ω · cm²/▪ 30 cm × 30 cm 1440 Ω · cm²/▪ 18.6 Ω · cm²/▪ 100 cm× 100 cm 15700 Ω · cm²/▪ 202 Ω · cm²/▪

[0249] It is desired that the width of the internal busbars should besmall so that the active area of the EC device can be maximized.Further, such narrow widths also minimize optical interference toviewing through EC devices to which such internal busbars areincorporated. Thus, narrow widths are less obtrusive to vision.

[0250] As used herein, unless specified to the contrary, the descriptors“narrow or wide” refer to a “width” dimension parallel to the surface ofthe feature being described, while the descriptors “thin or thick” referto a “thickness” dimension orthogonal to the surface of the featurebeing described.

[0251] A preferred geometry of the IB's include patterns which aregreater than about 1 μm in thickness, and most preferably greater thanabout 10 μm in thickness. Although any convenient material can be usedand formed by any convenient technology, materials and technologies thatallow such thick IB's to be deposited are preferred. Examples ofmaterials which are easy to deposit in these dimensions are typicallyconductive inks, pastes, and frits. Examples of the methods aredescribed below.

[0252] Generally, the overall conductivity of the substrate does notdepend appreciably on whether the conductive electrode coating is overthe grid, around the grid, under the grid, or in some such combination.In the present invention, if the grid is deposited on the surface of thetransparent conductor, the grid should be prevented from reacting orcorroding in the device through the use of a protective barrier orpassivation coating. The construction and materials of such a barriercoating depends upon the degree of reactivity of the grid material atthe potentials encountered during device operation.

[0253] The internal busbars of the present invention may not be directlyconnected to other busbars such as edge busbars or such signal leads.The internal busbars of the present invention can be termed“floating”busbars. The signals are generally conducted to the internalbusbars of the present invention by the conductive layer that is incontact with them. By such contact, the conductive layer's conductive iseffectively lowered because the internal busbars of the presentinvention have lower conductivity than the conductive layer they are incontact with. The IB's of the present invention can be optionallyconnected to other busbars described above, to other IB's, or toelectrical leads. However, as discussed below, an IB of the presentinvention can nevertheless receive an applied signal by the IB's being“bridged” to other voltage sources through the conductivity of theconductive layer the IB is in contact with. There are applications suchas, for example, those that call for specific signals being applied tospecific internal busbars where the internal busbars of the presentinvention can optionally be directly connected to a signal source.

[0254] In addition to a variety of lateral geometries, the IB's canoccupy a variety of transverse locations in a device. For example, apattern may be deposited on top of the TC. In a device of the form

Glass|TC1|electrolyte/redox species|EC|TC2|Glass

[0255] (where EC refers to an electrochromic film), for example, one maydeposit a grid pattern on TC1, on TC2, or on both TC's. Naturally, theheight of a grid on TC1 should be significantly less than the cell gap(i.e., the thickness of the electrolyte/redox species medium),preferably much less. For a grid deposited on TC2, one must ensure thatthe thickness, morphology, and chemistry of the grid do not adverselyaffect the EC film. Regarding thickness, if the thickness of the grid ismuch less than that of the EC film, then the grid has little effect onthe shape of the EC film. If the thickness of the grid is on the orderof or greater than that of the EC film, then the EC film may often forma noticeable “relief” of the grid pattern (or it may even form inseparate areas defined by the grid pattern).

[0256] The durability of devices with the IB grid of the presentinvention generally should be similar to devices without the IB grid.Any durability test should yield the same result with or without thegrid. That is, the addition of the internal busbars of the presentinvention should not affect the reliability and durability of thedevices. Accordingly, results of any durability tests to qualify adevice for a particular application are likely transferable, or can beanticipated to be the same if such tests are repeated with the deviceshaving internal busbars. Because durability is one of the key issuesinvolved in developing a commercially viable device, this is animportant parameter. To ensure durability of these devices, it has beendiscovered that it is preferred to deposit a passivation layer on top ofthe internal busbars, particularly if the IB's are deposited on top ofthe transparent ECE's. Materials for passivation are described below.

[0257] As shown in FIG. 21, the “effective height” of the grid may bereduced by embedding the grid conductor partially in the TC andsubstrate. Internal busbar conductors 2102 are embedded in substrate2101. The formation of internal busbar conductor 2102 may be done by anyconvenient way such as, for example, by etching or ablating away adesired pattern in the substrate and then depositing the desired gridmaterial. The effective height of the grid may be reduced by embeddingit partially in the glass as well as the TC. One can etch or ablate awayconsecutively the TC coating and the substrate, followed by depositingthe desired grid material. Alternatively, one can deposit the grid onto,or embed the grid into, the glass before the TC is deposited. Theportion of busbar conductors 2102 that are above the surface plane ofsubstrate 2101 is removed until the surface and the busbar conductorsare at substantially the same plane 2103.

[0258] In one embodiment, the grid is partially embedded into the glassand then the surface is planarized by, for example, polishing to producea structure as shown in the process in FIG. 21. Planarizing may also bedone by depositing additional material on to the substrate so that thetop surface of this added material is coplanar with the grid. AlthoughFIG. 21 shows conductors 2102 having circular cross section such ascommonly found in a wire, it could be of another convenient shape, suchas rectangular. Additionally material can be deposited, for example,from solutions, or by physical vapor deposition, etc. Some examples ofsuch materials are polyimide, sol-gel deposited oxides andorganic/inorganic hybrids.

[0259] A TC is then deposited on the resulting planarized surface andthe resulting glass|TC substrates used in the same manner as they aretypically used. This process of the present invention has the distinctadvantage that the more chemically active components of the device suchas the EC film and the electrolyte are not directly exposed to the IBgrid material.

[0260] Except for the glass substrates, the layers in single substratedevices (See, for example, FIG. 1E) are generally each quite thin(typically in the 100's of nm). It is therefore particularly preferredto use IB's which are fully embedded under the TC in such devices. TheIB on the outer TC (layer 103′ of FIG. 1E) could consequentially be ofany thickness since it will protrude on the outside of the device.

[0261] Whether it is desirable to include IB's on one or both TC's in adevice depends on a variety of factors, including the required responsetime and coloration uniformity characteristics and the cost ofmanufacturing the devices. Devices generally display faster responsetimes and greater coloration uniformity with the IB's implemented onboth TC's.

[0262] IB Dimensions

[0263] The dimensions of the IB's width and depth can be variedthroughout a substrate. As shown in FIG. 22, EC device 2210 hasconductive transparent substrate 2201 transversed by narrower internalbusbars 2202 and wider internal busbars 2203. Narrower internal busbars2202 and wider internal busbars 2203 are separated by gaps 2208 fromedge busbar 2204. Gaps 2208 are bridged by conductive transparentsubstrate 2201. Narrower internal busbars 2202 and wider internalbusbars 2203 optionally connect directly to edge busbar 2204.

[0264] By combining, for example, narrow and wide IB's one can enhancethe conductivity of the substrate while maximizing its transmission.However, while incorporating the use of wider IB's decreases theirresistance (and thus advantageously decreases the effective resistanceof the TC), it also affects the apparent transmission of the device. Thetransverse or primarily transverse direction is usually the direction ofmost importance for the optical properties of the devices. Accordingly,increasing the depth (or height) of the IB's is advantageous whencompared to increasing the width of the IB because increasing the depthwill typically have a much smaller adverse effect on the cosmeticappearance and/or the apparent transmission of the devices thanincreasing the width.

[0265] Another component of the present invention is the use of IB'swhich will be optically less prominent, by making the IB's much deeperthan they are wide. For example, defining the aspect ratio, r_(1b), asthe effective width of the internal busbar structure divided by itseffective height (thickness), it is generally desirable to have r_(1b)smaller than 1, for optical transmission applications where a viewingpath is through the surface on which is deposited the busbar structure.

[0266] The reason is that, if one is viewing parallel to the height(thickness) of the IB, then increasing the thickness while the otherdimensions of the IB remain constant does not substantially affect theappearance of the device; but such increased thickness does desirablyreduce the resistance of the IB (and therefore desirably reduces theeffective resistance of the corresponding TC). It is therefore generallydesirable that the height direction of the IB's be parallel to theprimary viewing direction for such applications.

[0267] Most commonly, this means that the height direction of the IB'sshould be transverse to the plane of the substrates of the device. Butfor some devices such as, for example, an automotive windshield, theprimary viewing direction might be at some angle to the approximateplane of the windshield. In such applications it would be preferable toimplement the IB's such that their height direction is parallel to suchslanted viewing direction. As shown in FIG. 23, device 2301 has internalbusbars 2302 embedded in substrate 2303 at an angle parallel to theviewing direction 2305.

[0268] Another consideration is the need to provide a contiguous channelwithin the device that allows the electrolyte fluid to flow throughoutthe gap during filling in order to minimize manufacturing difficulties.Referring to FIG. 31A, a device 3101 has internal busbars 3102 disposedsuch that no internal busbar blocks a contiguous channel. Internalbusbars 3102 are in contact with only one device edge and extend only tothe other device edge, thereby forming a contiguous channel 3103. If thedevice is filled with the electrolyte after edge sealing (such as byvacuum back-filling), only one fill hole is required to perform thefilling task.

[0269] Similarly, FIG. 31B shows a device 3110 where internal busbarscan extend from one device edge to the other device edge. The internalbusbars are arranged in a staggered configuration. Consequently,although internal busbars 3102′ might extend from one device edge to theother device edge, and each internal busbar 3102′ might be thicker thanone half the gap distance, their staggered arrangement forms acontiguous channel 3103′ which allows easy filling of device 3110, withelectrolyte fluid, without interruption.

[0270]FIG. 31C shows a device 3120 which has internal busbars 3102″ thatcan extend from one device edge to the other device edge, and that canbe in an overlapping relation. Internal busbars 3102″ are, however, inalternate ramped geometries which form a contiguous channel 3102″ whichallows easy filling of device 3120, with electrolyte fluid, withoutinterruption.

[0271]FIGS. 31B and 31C show embodiments of the present invention inwhich the sum of the thicknesses of the internal busbars is larger thanthe cell gap distance. Yet, the innovative geometries of the presentinvention allows such internal busbars' use without any problems ofelectrical shorting or interrupted electrolyte fluid continuity. Asdescribed above, the width of the internal busbars should be small sothat the active area of the overall EC device can be maximized. Theresistance of internal busbars with narrow width can be nonetheless lowbecause the height (thickness) of the internal busbars can be madeeffectively thick. As described above, geometries and patterns that formIB's having thicknesses greater than about 1 μm are preferred, and mostpreferred are thicknesses greater than about 10 μm. FIGS. 31B and 31Cshow how such thicker dimensions can be used without causing the gapdistance to be disadvantageously thick.

[0272] Auxiliary Uses for IB's

[0273] The IB's included in devices under the present invention may beused for additional purposes, and these may or may not requiremodification of the IB design. For example, the IB's may be used asJoule heating elements for purposes such as de-fogging. For thispurpose, it is desirable to pass current through the IB's independentlyof current being used to color or bleach the device.

[0274] One means for implementing this purpose according to the presentinvention includes providing for separate addressing of the two ends ofa set of IB strips. FIG. 24 shows a device 2410 with an EC assembly 2401having two internal busbars 2402 over the layers of TC 2403. Applying avoltage V1 and V2 of equal values across the two ends will induce acurrent flow along each of the internal busbars 2402 but will not resultin EC activity in device 2410 because, with equal voltage potentials ateach end, there is no current path or potential drop transverse to thedevice. If it is desired that EC activity and heating occurcontemporaneously, the signals can be adjusted accordingly to providefor a current path and a potential drop transverse to the device bychanging V1 and V2 to be unequal. For most EC devices the voltagedifference needed between V1 and V2 is less than 2 volts.

[0275] If IB's are implemented on both TC's of a window-type device,separate heating of both TC's without inducing EC activity requiresbalancing of the lateral voltage potentials so that there is notransverse potential. If simultaneous coloring is desired, thepotentials can be adjusted accordingly.

[0276] The IB's may also be used as antennae for electromagneticsignals. For example, one can use a strip IB as a monopole antenna,letting one end float electrically and connecting the other end to theappropriate signal processing electronics such as, for example, a radioreceiver. To obtain a larger signal, the signals from a set of stripIB's forming well known antennae geometries may be combined and thecombined signal appropriately processed. Other patterns of IB's formingwell known antennae geometries may be used to optimize the antennafunctionality. If desired, IB's may also be used as transmittersfollowing well known transmitter grid geometries.

[0277] IB's may also be used to provide or enhance the effectiveshielding from unwanted electromagnetic waves or interference. Thepenetration depth (or “skin depth”) of electromagnetic waves into thedevices may be decreased by increasing the effective conductivity of theTC layers. In addition, specific IB patterns may be employed such as,for example, forming a part of a Faraday cage to provide optimalshielding for a particular class of electromagnetic waves.

[0278] Separately-Addressable IB's

[0279] In an embodiment of the present invention, IB's form a singleaddressable array. FIG. 25A shows a device 2501 with internal busbars2505 arranged at an angle to and proximate to a busbar 2507 withproximate gaps 2508 between busbar 2507 and each internal busbar 2505.Proximate gaps 2508 are bridged by conductive layer 2509 on substrate2510. Busbar 2507 can be an internal busbar or an edge busbar. Busbar2507 and internal busbars 2505 form a single addressable array 2503powered by a conductor 2504. Optionally, each internal busbar 2505 isdirectly connected to busbar 2507.

[0280] In another embodiment of the present invention, the IB's are madeto be separately addressable. FIG. 25B shows a device 2502 withseparately addressable internal busbars 2506, each separately powered byseparate conductors 2504.

[0281] One can use the separately addressable IB's to obtain an addedmeasure of control over the spatial distribution of the coloring and/orbleaching of an EC device. Whether one needs to be able to addressseparately the IB's on one of the TC's or on both of the TC's dependsupon the degree of control required.

[0282] One can utilize the separately addressable busbars (or separatelyaddressable busbar groups) to have an EC device (e.g., a sunroof orwindshield) that has differential coloration from one side to the other,or from top to bottom, etc. Such individual control can produce a numberof effects such as, for example, a gradient effect, a shade effect, or ageometric pattern effect.

[0283] One can employ light sensors and use the signals from the sensorsto determine the appropriate signals to apply to the separatelyaddressable IB's to obtain the desired spatial distribution of coloringor bleaching. For example, for an automotive sunroof, one can use lightsensors to effectively track the position and intensity of the sun andthen color more deeply the appropriate regions of the sunroof. Inaddition, information (obtained either automatically or manually)regarding the presence and positions of occupants of the automobile maybe combined with the signals from the light sensors to determine theappropriate signals to apply to the separately addressable IB's toobtain an appropriate coloring or bleaching pattern. The light sensorsshould be situated such that they provide effective indications of thelight intensity from a variety of directions. The presence and positionsof occupants of the automobile may, for example, be sensed viatransducers in the seats and/or by detecting the status of theseatbelts.

[0284] Under the present invention, a variety of “Smart Devices” can bemade by using the signals derived from a system of sensors to determinethe appropriate drive signals to be applied to theindividually-addressable IB's and edge busbars in EC devices.

[0285] Conductive frits are usually pastes and liquids (also termedinks) of a conductive material in a carrier. The carrier typically curesor typically is eliminated during a post-application process such assubjecting to elevated temperatures. Conductive frits for IB can bedeposited by any convenient method such as, for example, X-Y MotorPainting/Screening, Doctor Blading/Silk Screening/Circuit Printing,Chemical Vapor Deposition and Physical Vapor Deposition (CVD and PVD):

[0286] 1. X-Y Motor Painting/Screening: For certain conductivematerials, which are applied in the form of viscous liquids, aprogrammable X-Y table with a fluid dispenser may be utilized to applythe desired pattern to the substrate. The thickness and width of theconductive line is determined by factors such as the size of thedispenser tip opening, the viscosity of the fluid, the dispenser linepressure and the lateral speed of the dispensing tip relative to thesubstrate, and the distance between the dispensing tip and thesubstrate. Low viscosity molten metals may also be used for the busbars.These could be sprayed or processed by soldering or welding. Thesemethods could be assisted by ultrasound or other energy imparting meansto promote uniformity and/or better adhesion to the substrate.

[0287] 2. Doctor Blading/Silk Screening/Circuit Printing: This methodinvolves the forcing of a viscous liquid through narrow openings in anappropriate mask, to be deposited on a substrate in a pattern determinedby the mask design. This mask may consist of any type of tape, film, orother mask material, such as a silk-screen-like item, placed on top ofthe substrate, with channels or isolated voids in a desired pattern. Anexcess of the fluid is then placed at one end of the mask, then auniform, flat tool (such as a “squeegee” or similar implement) isdragged across the mask, forcing the fluid through the pattern troughsonto the substrate.

[0288] Another alternative is to silkscreen, or otherwise use a doctorblade to deposit uniform layers of photoprintable thick filmcompositions. The internal busbar pattern is then formed by exposing thedeposited film to certain wavelengths of light through masks andfollowed by chemical processing. The passivation materials for internalbusbars such as certain dielectric materials can be similarly processed.The advantage of this over conventional silkscreening is to get finerresolution and/or higher densities of conductive lines.

[0289] 3. Chemical Vapor Deposition and Physical Vapor Deposition (CVDand PVD): CVD is a known process which deposits a coating by decomposinga chemical vapor to provide the depositing material. PVD is a knownprocess which deposits a coating by vaporizing a material and thenredepositing this in a substrate in a vacuum chamber. CVD and PVD may beassisted by energy imparting sources such as plasma, ionized beams,microwave, etc.

[0290] In these methods, patterns are applied by placing either a shadowmask over the substrate and coating directly onto the surface, or byusing photolithographic technology to apply a photoresist mask to thesubstrate, coating that assembly with metal, and then stripping thephotoresist layer away, leaving the metal pattern.

[0291] Some exemplary frit, inks and conductive adhesives that may beemployed in this invention include:

[0292] Frits

[0293] DuPont Electronic Materials, Wilmington, Del., Silver-BearingConductors: DuPont Silver Thick Film Composition, Nos. 1991, 1992, 1993,1997; DuPont Silver Thick Film Composition, #7713; and DuPont SolametPhotovoltaic Compositions such as #E64885-52A.

[0294] DuPont Gold-Bearing Conductors.

[0295] DuPont Fodel Photoprintable Conductors DC201 and DC010.

[0296] Ferro Silver Paste FX 33-246 available from Ferro Inc., SantaBarbra, Calif.

[0297] Metal Inks

[0298] Engelhard Electronic Materials, East Newark, N.J.,Metallo-Organic Inks: Platinum Inks such as #05X, Gold Inks such as#A3622, and Silver Inks such as #R2/321 and low temperature curedflexible materials such as #M5860.

[0299] Conductive Epoxies, Silicones, etc.

[0300] Grace Specialty Polymers, Emerson & Cuming Inc. (Woburn, Mass.),Minico M 4200 Flexible Silver Buss Bar; 4xxx series materials; EccocoatCT 5030 A/B Flexible/Rigid Buss Bar; Minico M 6xxx series silver/coppermaterials.

[0301] When devices are fabricated that use two substrates, such asthose described in U.S. Pat. Nos. 5,142,407, 5,241,411 and 4,761,061,one or both of the substrates may have added internal busbars accordingto the present invention.

[0302]FIGS. 26A and 26B show two configurations of various grid patternsaccording to the present invention that do not extend to the edges. FIG.26A shows a device 2608 having a perimeter busbar 2602 on substrate2601. Substrate 2601 has a conductive layer 2615 on its surface. Aseries of internal busbars 2603 form a crosshatch pattern. Internalbusbars 2603 can be on, in, and/or below conductive layer 2615. Theperimeters of each internal busbar 2603 are in contact with conductivelayer 2615.

[0303]FIG. 26B shows a device 2609 having a series of internal busbars2604 forming a parallel pattern. Neither series of internal busbars 2603or 2604 touch perimeter busbar 2602. As a result, when an EC device isfabricated using two substrates, the grid pattern can be completelyenclosed in the device. The internal busbars conduct a current thattravels from the perimeter conductor through the conductive layer 2615to the internal busbar. This may be advantageous, since the adhesiveused to seal the edges of the two substrates need not be modified incomposition and no change in processing parameters is needed forensuring good adhesion to the internal busbars and for accommodating thechange in substrate topography.

[0304]FIG. 26C shows a device 2610 having a coiling internal busbar 2605which is in contact with conductive layer 2615 at the entire perimeterof internal busbar 2605. Coiling internal busbar 2605 has higherconductivity than conductive layer 2615, which serves to lower theoverall resistance of conductive layer 2615, thereby making morehomogeneous the applied signal to conductive layer 2615. Coilinginternal busbar 2605 can stand alone as shown. Coiling internal busbar2605 also can be formed in close proximity at its outer coil to aperimeter busbar (not shown). Alternatively, the coiling internal busbarcan be attached directly to a signal power by leaving a portion of thecoiling internal busbar exposed and attaching a signal wire to theexposed portion.

[0305] Since the current at the perimeter has to flow only through gapsof a short distance through the transparent conductors to the internalbusbars of FIGS. 26A, 26B, and 26C, the resistance drop will benegligibly small across such gaps. This use of the transparent conductorto connect an internal busbar to the primary busbar has not beendiscussed or disclosed in any prior art described above.

[0306] A passivation layer may be deposited using similar techniquesdescribed previously. If certain materials and methods are used todeposit the grid pattern such as silk-screening of metal frits, thenpost-treatment such as curing or hardening with time, heat, radiation(UV, visible, IR, microwave) may be required. The passivation layer istypically deposited after the above post-treatment. Similar types ofpost-treatment procedures may be required to harden the passivationlayer.

[0307] The post-treatment for the grid pattern may also result in anin-situ formation of a passivation layer on the surface. The in-situformed surface may consist of a phase separated inert material, anoxidize portion, a nitride portion, etc. This will also depend on theatmosphere and temperature conditions under which such post-treatment iscarried out. This passivation layer may be sufficiently passivating tobe incorporated in these devices. Treatment where a part of the exposedgrid pattern becomes passivated could also be done when the gridpatterns are deposited by physical and chemical vapor deposition. Thesurface of these may be passivated using oxidation, nitriding, heat,laser, plasma, or ion bombardment assisted treatments. The passivationlayer may consist of organics, inorganics or hybrid materials. Adhesivessuch as, for example, non-conducting epoxy adhesives, urethanes,acrylates, or polyesters could be deposited for passivation. These maybe the same materials that are used for making device seals. Thematerials may be cured by heat and/or radiation, such as UV, IR ormicrowave. The viscosity and the application procedure can be adjustedso that the desired thickness is obtained.

[0308] The materials can be applied by any convenient method such as,for example, being screened, dispensed, sprayed, or painted. Sol-gelmethods could also be used to deposit oxides and polyceramics aspassivation layers. Examples of such materials are alcoholic ornon-alcoholic based solutions of metal alkoxides, nitrides, halides, ormixtures thereof, or solutions of reactive metallic precursors withorganic complexing agents. Further, these oxides may be inert such assilica or could be conducting such as indium tin oxide and doped tinoxide. Preferably the passivating materials should be non-conductive,both ionically and electronically. Electronically conducting materialswhich may be used as passivating materials are those which are used inmaking transparent ECE's such as doped tin oxide and indium tin oxide.They should not also be attacked, swelled, or interact with the layersthat come in contact with such as electrochromic layers, ion storagelayers, electrolytes, etc. Examples of some commercialencapsulants/passivation layers that could be silk-screened include#A3840, #A3560, and #A3563, made by Engelhard. An example of aphotoprintable passivation layer is Fodel DG211 from DuPont ElectronicMaterials.

[0309] Electrochromic devices use several transparent conductors thatare not reactive while the other components such as electrochromiclayers, counterelectrodes, and redox materials in the electrolytenecessarily participate in the electrochemical activity required forelectrochromic operation. Thus, non-reactive materials are defined asthose that lie outside the electrochemical potential range that isutilized for operating the EC device. Also materials that are insulatorsand/or do not transmit or get intercalated with ions under the aboveoperating conditions and will not change their physical properties inthe cell (such as dissolution in the liquid electrolyte if used) canalso be considered as non-active. Materials such as many polymers suchas epoxies, polyimides, acrylics, urethanes, and inorganics such asdense silica, alumina, several other oxides, silicates, andorgano-silicates can be also considered non-reactive. For some devices,metals such as gold and platinum may also be considered non-reactive.Thus these metals may be used for busbars without additional passivationlayers. There may even be thick layers of transparent conductors such asITO, in a thickness that is conductive enough for the busbar, but nottransmissive enough to be called TC (transparent conductor).

[0310] For designs where the internal busbars extend to the perimeteredge of the substrate, the passivation layer may extend to the edge ofthe substrate, or stop short of the edge so as to only be in theinterior of the device. In the latter case, the internal busbars can beelectrically contacted with the edge busbars (for example by usingwires, tapes, conductive adhesives, solders, or wire clips). The noveledge busbars of the present invention may also be used in conjunctionwith the novel internal busbars of the present invention.

[0311] The conductivity of the substrate can also be enhanced throughthe use of a wire pattern embedded in a substrate (the substrate may beconstructed from glass, plastic, or some other material). This wirepattern substitutes for the grid pattern described above. If thesubstrate is essentially electrically insulating, and if the conductivepattern is entirely embedded in the insulating substrate, then it isgenerally necessary to connect electrically the conductive pattern andthe transparent conductor. This may be done, for example, by drillingholes though the substrate up to the metal grid and then filling theholes with a conductive material. FIGS. 27A, 27B, 28, and 29 illustratethis concept, including different methods of ensuring transparentconductor/plug contact.

[0312]FIGS. 27A and 27B show a device 2710 with a substrate 2705 coveredwith a transparent conductor layer 2704. Internal busbar conductors 2702are embedded in substrate 2705. Conductive plugs 2703 lead from thesurface of device 2710 to electrically contact internal busbarconductors 2702. In this example, transparent conductor layer 2704 wasapplied after the holes for plugs 2703 were made but before plugs 2703were formed.

[0313]FIG. 28 shows a device 2801 formed by attaching internal busbars2802 to a surface 2807 of a substrate 2803. Holes 2805 are formedeffective to extend from an opposite surface 2808 of substrate 2803 tointernal busbars 2802. Conductive plugs 2804 are formed effective toextend from internal busbars 2802 to opposite surface 2808. Transparentconductive layer 2806 is then formed on opposite surface 2808,contacting conductive plugs 2804, thereby being in electrical contactwith internal busbars 2802.

[0314]FIG. 29 shows a device 2901 where direct addressing of theinternal busbar conductor was not necessary. Device 2901 has an internalbusbar conductor 2902 embedded in substrate 2904. A conductive layer2903 provides electrical contact between transparent layer 2905 andinternal busbar conductor 2902. Inert filler plug 2906 fills the hole.Transparent conductor 2905 is applied after the hole that provide accessto internal busbar conductor 2902 is made. Then conductive layer 2903 isformed in the hole. Finally, inert filler plug 2906 is formed.

[0315] If the conductive pattern is not entirely embedded in thesubstrate (i.e., if it contacts the transparent conductor) or if thesubstrate is sufficiently conductive, a separate conductor is generallynot necessary.

[0316] Internal busbars can also be used to make devices with thosesubstrates on which only low conductivity transparent ECE's can bedeposited. Typically, transparent ECE's such as indium tin oxide anddoped tin oxide are deposited at high temperatures (in excess of 200°C.) to get good conductivity. Most of those materials, when deposited onplastics, at lower temperatures, are less conductive. Thus, the use ofEB's as described above in conjunction with lower conductivitytransparent ECE's would result in high conductivity substrates whichwill be attractive for electrochromic devices.

[0317] The Examples which follow are intended as an illustration ofcertain preferred embodiments of the invention, and no limitation of theinvention is implied.

Example 3

[0318] Strips of silver frit paste (DuPont # 7713) were deposited bysilk-screening onto a 3 inch×3 inch (7.5 cm×7.5 cm) TEC 15 substrate.The substrate was then heated under ambient atmosphere according to thefollowing four step procedure;

[0319] Step 1: Temperature raised from 25° C. to 100° C. at 10° C./minand held at 100° C. for 15 minutes.

[0320] Step 2: Temperature raised from 100° C. to 325° C. at 10° C./minand held at 325° C. for 10 minutes.

[0321] Step 3: Temperature raised from 325° C. to 600° C. at 10° C./minand held at 600° C. for 10 minutes.

[0322] Step 4: Temperature lowered from 600° C. to 25° C. at 10° C./min.

[0323] After firing the width and depth of the silver lines weremeasured using surface profilometry and found to be 0.2″ (5.1 mm) wideand 15 μm deep. The spacing between the lines was 1.0″ (25.4 mm).

Examples 4, 5, 6, 7, and Comparative Example 3C

[0324] The “TEC-Glass” products, commercially available fromLibby-Owens-Ford Co. (Toledo, Ohio), are manufactured by an on-linechemical vapor deposition process. This process pyrolytically depositsonto clear float glass a multi-layer thin film structure, which includesa microscopically thin coating of fluorine-doped tin oxide (having afine grain uniform structure) with additional undercoating thin filmlayers disposed between the fluorine-doped tin oxide layer and theunderlying glass substrate. This structure inhibits reflected color andincreases light transmittance. The resulting “TEC-Glass”product is anon-iridescent glass structure having a haze within the range of fromabout 0.1% to about 5%; a sheet resistance within the range of fromabout 7 to about 1000 ohms per square or greater; a daylighttransmission within the range of from about 77% to about 87%; a solartransmission within the range of from about 64% to about 80%; and aninfrared reflectance at a wavelength of about 10 μm within the range offrom about 30% to about 87%.

[0325] A TEC 15 substrate (3 inch×3 inch; 7.5 cm×7.5 cm) wassilk-screened with silver paste as described in Example 1, where thelength of the silver strip was incrementally varied in such a manner asto leave an equal distance between edges, at right angles to the strips,of the glass substrate as shown in FIG. 26B. The distances of the silverstrip from the edge for Examples 4, 5, 6, and 7 are 0.0 mm, 1.0 mm, 3.0mm, and 7.0 mm respectively. The resistance of the substrate wasmeasured by soldering a metal strip 2 mm wide at both edges of thesubstrate which were at right angles to the internal silver strips toserve as a representative portion of a perimeter busbar. By applying avoltage across the soldered strips the resistance was measured fordifferent increments of distance of the silver strip from the perimeterbusbar. The results are listed in the following Table 3. TABLE 3Distance of Silver Strip Resistance of From Edge Substrate Example (mm)(Ω) 4 0.0 0.1 5 1.0 1.2 6 3.0 1.9 7 7.0 3.2

[0326] The Comparative Example 3C, a TEC 15 substrate with no internalsilver busbars had a resistance of 15 Ω. By comparison, as shown in thetable, Example 4, the substrate with internal silver strips extendedfully to the perimeter busbars had a resistance of 0.1Ω. Even in Example7, with the silver busbars as far as 7 mm from the perimeter busbar, theresistance is decreased to 3.2 Ω from the Comparative Example's 15Ω.

Example 8

[0327] Internal silver busbars were prepared as described in example 3,except that after the four step firing procedure the metal strips wereover-coated with an epoxy based polymer for passivation and cured at120° C. for one hour.

Comparative Example 4C

[0328] A 3″×3″ (7.5 cm×7.5 cm) TEC 15 substrate coated with 380nanometers of WO₃ according to the method set forth in U.S. Pat. Nos.5,252,354, 5,457,218 and 5,277,986 and a counter electrode of TEC 15 ofsimilar size was made into a cell using an epoxy seal containing 210μmspacers. The two electrodes were positioned so that they were slightlyoff-center exposing a region at either end for application of a metallicbusbar. Prior to assembly the counter electrode had two holes drilled init for application of the electrolyte. The cell was filled withelectrolyte containing 0.01M LiClO₄ and 0.05M ferrocene in a 60:40volume % mixture of propylene carbonate and tetramethylene sulfone andthe fill holes plugged with epoxy. The conductive surfaces whichprotruded from either side of the cell were ultrasonically soldered withlead-tin-cadmium-based solder. Wires were then attached to thesecontacts. The electrochromic performance of the device was determined byplacing the cell in a spectrometer and following the color kinetics at550 nm while applying a coloring potential of 1.3 volts followed by ableaching potential of −0.3 volts. In the transmissive (bleached) statethe cell had a transmission of 77% and in the fully colored state atransmission of 10% T. At a coloring potential of 1.3 volts the celltook 46 seconds to color from 70% T to 10% T and 47 seconds to bleachback to 70% T.

Examples 9, 10, 11 and Comparative Example 4C

[0329] Four electrochromic cells were prepared as described incomparative Example 4C where the composition of the electrodes werevaried as follows;

[0330] Cell A, Comparative Example 4C, had conductive electrodes with nointernal busbars.

[0331] Cell B, Example 9, had internal busbars on the working electrode(WO₃) only.

[0332] Cell C, Example 10, had internal busbars on the counter electrodeonly.

[0333] Cell D, Example 11, had internal busbars on the both electrodes.

[0334] In all cases, Examples 9, 10, and 11, the internal busbars weredeposited as described in Example 8. The cells were colored at 1.3 voltsfor 90 seconds and bleached at −0.3 volts for 90 seconds. The colorkinetic data for the cells is shown in the following Table 4: TABLE 4Time to color from Time to bleach from 70% T to 10% T 10% T to 70% TCell Seconds Seconds Cell A 89 89 Cell B 74 65 Cell C 89 89 Cell D 56 58

Comparative Example 5C

[0335] An electrochromic cell was prepared as described in Example 8with conductive electrodes which contained internal busbars without apassivation layer. The cell was cycled at 70° C. at a color potential of1.3 volts for 15 seconds, long enough to colorize, followed by beingbleached for 45 seconds at −0.3 volts. After 5,000 such cycles the cellshowed visible reaction of the silver strips within the cell. Thisresulted in a degradation in the cell's optical properties.

Example 12

[0336] An electrochromic cell was prepared as described in Example 8,containing internal silver busbars, on both electrodes, with aprotective epoxy overcoat. At a coloring potential of 1.3 volts the cellcolored from 70% T to 10% T in 8 seconds. The cell was cycled at 70° C.under a coloring potential of 1.3 volts for 15 seconds and a bleachpotential of −0.3 volts for 45 seconds. After 5,000 cycles the cellshowed no visible reaction of the internal busbars in the cell nordegradation of the cell's electrochromic performance.

Example 13

[0337] Silver strips were deposited onto TEC 15 as described in example3, and overcoated with a layer of indium tin oxide (ITO). The ITO wasdeposited by electron beam (E-beam) evaporation and deposited directlyon top of the TEC 15 and the silver strip lines through the use of amask. The E-beam target was an indium tin oxide composite and thethickness of the ITO layer thus formed was 500 nm. Two of these TEC 15substrates having the described electrodes were used to make anelectrochromic cell as described in example 9. Under a coloringpotential of 1.3 volts the transmission at 550 nm changed from 76% T to8% T. It took 14 seconds to modulate from 70% T to 10% T at 1.3 volts,while it took 23 seconds to bleach back to 70% T at −0.3 volts.

Example 13B

[0338] Silver strips were deposited onto TEC 15 as described in example3, and overcoated with a layer of Sol-Gel derived antimony doped tinoxide (ADT). The ADT precursor was prepared as described in U.S. Pat.Nos. 5,525,624 and 5,457,218. The electrodes were made into anelectrochromic cell as described in example 9. At a coloring potentialof 1.3 volts the cell colored from 70% T to 10% T in 19 seconds. At apotential of −0.3 volts it bleached back to 70% T in 20 seconds.

Example 14

[0339] Fodel materials and processes (from DuPont) and the like can beused to deposit busbars which are less than 100 μm in width. These linesare practically invisible to the eye, depending on the distance betweenthe eye and the substrate on which the lines are deposited. For example,a normal eye subtends a small enough angle with lines of widths of 100μm from a distance of 19 inches that the line is not discernible (about0.01 degrees). Thus, any angle equal to or smaller than 0.01 degrees canbe considered as invisible. Such busbar widths that form these angles,depending upon the distance of the substrate from the observer, can beutilized with little or no interference with vision. For example, 50 μmwide lines (6 μm thick) spaced at a distance of 0.75 cm are expected togive the same overall conductivity to the substrates as lines which are100 μm wide (6 μm thick) and spaced 1.5 cm. Both of these widths andline spacings are expected to give photopic transmissions in excess of70% when deposited on conductive glass (such as TEC glass from LOF) witha resistance of 8 or more ohms/square.

[0340] Although the above description is for chromogenic windows, theseprinciples can also be utilized to develop non-chromogenic windows whichcan be defrosted by applying an electrical voltage at the edges butwithout any visible obstruction from conductors in the center of thewindow. These windows can be used in various applications wherefrost-free characteristics are desired. Examples of such application arein aircraft and automotive windows and mirrors. For an automotivewindshield, these can be deposited on glass before lamination. Afterlamination, preferably these lines reside inside of the laminated areaso that they are not scratched. They can also be used for other windowsand mirrors which are not laminated, and to further enhance theirscratch resistance they may be coated with hard transparent materials(for example, see U.S. patent application No. 09/099,035, filed Jun. 18,1998, which is incorporated herein by reference). Since hightemperatures (typically 500 to 800° C.) are required to fire theselines, this could be accomplished simultaneously while the glass isbeing bent and/or strengthened (or tempered) which may be necessary forthese products. As described above, based on the angular calculations,widths of these lines can be wider for rear automotive windows ascompared to the windshields, since the latter are closer to theobserver. Further, the material in these widths can also be used todeposit antennas on glass (such as automotive windows) which areinvisible, i.e., the window appears transparent although a patternedantenna is printed using these conductors and processes.

Example 15 and Comparative Example 6C

[0341] Two 6″×3″ (15 cm×7.5 cm) sized electrochromic cells wereprepared. TEC 15 was used as the transparent conductor in each cell.Example 15 had an internal busbar while Comparative Example 6C did not.The cell without the busbar, Comparative Example 6C, was assembledsimilarly to the assembly described in Comparative Example 4C. Thespacing between the substrates, however, was 88 micrometers. The twoelectrodes were positioned with an offset so that about 0.25 inch (0.63cm) of each electrode strip, at either of the 3″ (7.5 cm) ends of thesubstrates, was exposed. To these exposed edges, a solder was applied bya heated ultrasonic soldering system (Sunbonder from Sanwa ComponentsUSA, San Diego, Calif.). The solder used was Cerasolzer 186 (obtainedfrom Sanwa Components US), and had an average thickness of about 20micrometers.

[0342] The second cell, Example 15, also had a gap 88 micrometers thickand was made with both internal busbars and edge busbars as taught inthis invention. In Example 15, edge busbars and an internal silver fritbusbar were applied to three contiguous edges, via an x-y dispensingtechnique, similar to that shown in FIG. 33A.

[0343] The frit layers were fired with the four-step procedure as inExample 3 and then passivated as in Example 8 using a black coloredbisphenol A based epoxy adhesive. This frit/passivation pattern wasapplied to both the substrates. The width of the frit line was about 0.7mm and thickness of the frit line was between 10 and 15 micrometers. Thethickness of the passivation layer was about 30 to 40 micrometers with awidth of about 1.5 mm so as to completely cover the frit to form anencapsulation around the frit. One of the substrates was then coatedwith tungsten oxide, assembled, and filled as described in theComparative Example 4C. The frit pattern was identical on both thesubstrates except that the frit line pattern was lightly offset so thatthe frit lines on the two substrates were next to each other rather thanopposed or on top of each other. This was done to ensure that any localbumps would not lead to any electrical shorting and that the cell gap ismaintained at 88 micrometers.

[0344] Similar to that geometry shown in FIG. 33B, the internal busbarwas formed by one of the frit lines, while the other three frits formedan edge busbar since they were outside the cell seal area. Further, thesoldered busbar which was applied in addition to the frit busbar on theedge, reinforced the conductivity on that edge, while providing a meansto attach a soldered electrical lead. The silver frit and the solderedbusbar were touching each other in this Example.

[0345] Example 15 and Comparative Example 6C were colored at 1.3 voltsfor 60 seconds and bleached at −0.3 volts for 60 seconds. The plots oftransmission versus time are shown in FIG. 34A, and the concomitantcurrent flow through the devices is shown in FIG. 34B. In FIG. 33B,DuPont Frit type 7713 was used to form the frit layers. It can be seenthat in Comparative Example 6C, the cell without the internal busbar,the coloring reaction is slow and the depth of color is small. Bycontrast, in the cell with the internal busbar, Example 15, the coloringand bleaching reactions are faster and the depth of coloration is muchhigher because the internal busbars are able to supply much higherlevels of current when needed during coloration and bleaching. Thus,devices that demand high currents any time during coloration orbleaching will particularly benefit from this invention. Typically, ECdevices requiring currents in excess of 0.1 mA during coloration orbleaching will benefit most.

[0346] Intermittent Potential Circuitry

[0347] As described previously, the coloring voltage only needs to beapplied intermittently, depending on the length of the color statememory, after sufficient coloration has been achieved. For example, ifthe memory of the device was longer than the color duration required forthe particular application to be colored, then the coloring potentialeffectively could be applied just once and then turned off (i.e., thedevice is left in non-powered open circuit mode). The potential can thenbe applied again when the device's light transmission needs to change,e.g., while bleaching or changing its transmission to a differentdesired level. However, under certain circumstances, it might benecessary to keep the device in a desired state of transmission forperiods that are longer than their color state memory.

[0348] In the present invention, consider for example the case where acoloring potential is initially applied which is removed after thedevice attains the desired color, i.e., the device is kept in an opencircuit. The device is thus allowed to gradually bleach with time, for aperiod t₁, as a result of its limited color state memory. Before thedevice completely bleaches, the coloration potential is reapplied for aduration of time t₂. This process can be continued indefinitely for aslong as the device needs to be kept in the particular colored statebefore a different voltage is required to be applied to change thedevice's light transmission (e.g. bleach potential).

[0349] The period t₁, after which the coloration voltage is re-applied,depends in part on the extent of color change that is allowed before itmight become obvious to the user that the device light transmission ischanging. This allowable change in photopic transmission, all measuredat 550 nm, for a window in a building or a car (e.g., a sunroof) ispreferably in the range of from about (the difference (T_(c1)%-T_(c2)%),as in FIG. 35) 0.1% to about 20%, more preferably from about 1% to about15%, and most preferably from about 5% to about 10% from the desiredcolored state. The above transmission criteria can also be used wherethe devices only color in the near infrared region, about 0.7 μm toabout 2.5 μm. The change in light transmission can be solar transmissioninstead of photopic transmission. Furthermore, the light transmissionwavelength can be selected in any conveniently selected range.

[0350] The process of this invention is explained referring to FIG. 35,where transmission vs. time and applied voltage vs. time is plotted fora typical EC device controlled by the present invention. A voltage V_(c)is first applied to colored the window (as shown by the transmission T %falling, indicating that the light transmission is low). The voltage isthen removed, as shown by a break in the voltage line, for a period oft₁. During this time t₁, the cell starts to bleach, as shown by thetransmission T % rising. The time ti is related to the length of thecolor state memory for a particular EC device. To keep a window colored(after initial coloration), the coloring potential is reapplied for aperiod of t₂ followed by the removal of power (holding period) for aperiod of t₁. This alternating sequence is continued indefinitely, foras long as it is desired to keep the device in that desired state oftransmission. The desired state is a range of transmission defined byT_(c1)% and T_(c2 %). In this case, the total time t_(C) is the overalltime of coloration.

[0351]FIG. 35 also shows that the initial coloring voltage can beapplied as an increasing linear ramp to a maximum potential V_(c).Alternatively, a step potential V_(c) can be applied. Another way toapply the potential is by imposing a maximum curent limitation. Eitherof these two modes, or a non-linear ramp, could be conveniently used.With increasing device area, it may be preferred to ramp the coloringand bleach potential so that the current densities at the edges can belower. This also promotes a spatial uniformity in color change duringcoloration and bleaching. This is particularly noticeable as the devicearea increases. Also during the interval t₂, the coloration potential(V_(c)) could be applied as a step potential (as shown), or it may beramped from the open circuit potential of the device to V_(c). It mustbe noted that V_(c) or V_(b) referes to the potential which the powersupply attempts to apply to the EC cell and is also the limitingpotential on the EC cell. Hence the EC cell has charateristics of an(RC) circuit, the potential of the cell (V_(cell)) only changes slowlyas shown by the dashed line in FIG. 35.

[0352] One of the more important variables that affects t₁ and t₂ is thedevice temperature. As an example, depending on the EC device and thecomponents used, t₁ at −20° C. could range from a few hours to severaldays or even months, while t₁ at 70° C. could change to range from about1 to about 15 minutes. Similarly, t₂ at −20° C. could range from about 1to about 60 minutes, while changing to range at 70° C. from a fractionof a minute to about 10 minutes. Further, the change in these timesmight not be linear with temperature.

[0353] It is understood that for certain situations, t₁ and t₂ can befixed as in the prior art; but in this invention these time intervalscan be allowed to change as discussed above, unlike the prior art.

[0354]FIG. 35 also shows that even the bleach time (tB) could depend onthe device temperature or/and on the total time the device was kept inthe colored state (t_(c)) prior to initiating the bleach.

[0355] Typically both t₁ and t₂ decrease with increasing temperature.Thus, incorporation of a temperature sensor which provides a feedbackinto the control circuit could be used for this purpose. The temperaturesensor may be any convenient sensor such as, for example, a thermistor,a RTD thermocouple, a transistor, or a diode, the output from which canbe used to determine t₁ and t₂.

[0356] For example, referring to FIG. 36A, in the case where a timer isused to provide the t₁ and t₂ circuit functions, the thermistor wouldpreferably be a negative thermal coefficient (NTC) thermistor. When thetemperature increases, the resistance of the NTC thermistor woulddecrease and the resulting RC product (R is resistance, and C iscapacitance) connected to the LM 556 (National Semiconductor, SantaBarbra, Calif.) timer would also decrease leading to smaller t₁ and t₂.The drop in resistance in the NTC thermistor with temperature would becorrelated with the transmission changes during t₁ and t₂ periods of theEC device.

[0357] Preferably, the temperature coefficient of the thermistor and thecapacitor in the circuit should be chosen so that the change in RC wouldnaturally mimic the desired change trends needed for t₁ and t₂. One mayeven employ two thermistors in conjunction with two capacitorsrespectively, where the parameters of one set of resistors/capacitorsare tailored to correspond with the changes in t₁ and the other set ofresistors/capacitors corresponds with the changes in t₂.

[0358] In a variable coloration device, t₁ and t₂ will depend on thedepth of coloration. For example, in the open circuit mode thetransmission change for a deeper colored state may be faster (thusrequiring a shorter t₁) than for a shallower colored state. Similarly,it may take more time to achieve a darker state (thus requiring a longert₂) Since the depth of coloration is typically related to the potentialused for coloration, one could define and store in the control circuit aprofile of t₁ and t₂ values that are calibrated with the appliedcoloration voltage.

[0359] As the device ages, t₁ and t₂ may also shift. Account could bekept of the number of cycles, time spent in a particular state oftransmission or any other convenient method which keeps a track of theage and usage of the cell. An aging profile with varying t₁ and t₂ couldbe used to drive the cell and if needed, the potential can also bevaried and controlled to keep the initial level of coloration. Suchcontrol can be by any convenient method such as, for example, the use ofmonitoring sensors and feedback processes.

[0360] In another aspect of this invention, no prescribed periods areused but rather the actual level of coloration is sensed through the ECcell. In this case where one or more photosensors are used, the degreeof color change can be detected by the photosensor and once thecoloration has changed to a predetermined level, the necessary voltagecan be applied to recolor the EC cell back to its original depth. Use ofthe photosensor can also eliminate any need to pre-program values of orfactors to calculate t₁ and t₂ with aging, temperature or colorationvoltage.

[0361] Photosensors, e.g., CdS photoconductors on Si photodiodes, can beused to provide feedback signals for controlling t₁ and t₂ instead ofpresetting fixed values for t₁ and t₂. In this case, the photosensor(s)would monitor the transmission of the EC cell and actively signal thecircuitry as to the appropriate times to remove and to apply thevoltage. As coloration rates and bleach rates change with temperature,aging, and other factors, t₁ and t₂ are adjusted accordingly. Preferablya pair of photosensors are used. One photosensor is placed on top of thecell to obtain the baseline for incoming light while another is placedunderneath the cell to collect the transmitted light. The electricalsignals from these two photosensors are then connected to a differentialamplifier, the output of which is proportional to the relativetransmission through the cell. Depending on the sensed output, the cellwill be subjected to open circuit (holding period t₁) or voltageapplication (period t₂).

[0362] Further, as the cell ages thereby affecting its coloring andbleaching kinetics, the depth of coloration can still be maintainedsince t₁ and t₂ will change due to the feedback provided by thephotosensors. For example if the coloration rate of the cell slows down,both t₁ and t₂ will increase to maintain a pre-determined differentialoutput from the photosensors for identical illumination conditions.Also, if t₁ and t₂ become longer than pre-determined “acceptableperiods”, then the circuit may be configured to increase the colorationpotential (subject to a maximum safe-potential for the devices) toincrease the coloration speed.

[0363] Another method monitors the current (I) or the rate of change incurrent injected with time (t), i.e. dI/dt. Once dI/dt reaches aprescribed low value, the coloring potential is removed.

[0364] The transmission change during the holding period (t₁) can alsobe correlated to the open circuit potential change between the two cellelectrodes. During the holding period (tl), the potential between thetwo opposing electrodes of the EC cell (V_(cell)) will also decrease.Once a predetermined change in this voltage (ΔV) is reached, a coloringvoltage can be then applied to recolor the EC device. The time period t₂can be determined by checking the current being injected into the cell.For example, as shown in FIG. 34B, for a constant voltage the rate ofchange of the current decreases with time and reaches a limiting value.Thus, when the change in the current with time becomes smaller than apredetermined level, the coloring voltage can be removed.

[0365] Alternatively instead of monitoring dI/dt, just the current (I)could be measured. Once the absolute value of the current is below apredetermined limit the coloring voltage is removed. As describedearlier, this method also self compensates for any changes in cellkinetics, caused by aging, by increasing time periods t₁ and t₂ duringthe coloration period. When these time periods become longer thanpre-determined “acceptable periods”, the circuit if desired may beconfigured to increase the coloration potential (subject to a maximumsafe potential for the devices) in order to increase the colorationspeed.

[0366] Alternatively, the charge injected during coloration can bemonitored by a charge integration circuit. Once a predetermined chargehas been injected, the coloration voltage can be removed. For many ECdevices, the charge passed into the device for a desired level ofcoloration may depend on temperature. One method to take into accountwhere this charge will increase with temperature is to have a comparatorwith a thermistor-containing reference. All of the control parameterswhich determine t₁ and t₂ such as T_(c1)%, (T_(c1)%-T_(c2)%), ΔV, I, anddI/dt may be fixed and/or varied with temperature and/or aging of thedevice. One may also determined t₁ or t₁ by measuring the voltage at theEC cell V_(cell) and comparing this with the V_(C) or V_(B). Duringcoloration V_(cell) asymptotically approaches V_(c). When V_(cell) iswithin 5% (preferable 1%) of V_(c), the coloring potential V_(c) isremoved to let the cell rest in open circuit conditions. Alternatively,V_(c) could be continued to be applied for an additional fixed timeafter the above condition is met to allow the cell to reach equilibrium.The total coloration time (t₁ or t₂) are obtained by adding the time forcoloration during which V_(cell) approaches V_(c) and the fixed durationdescribed above. During the open circuit mode (e.g., in coloration) thepotential of the cell (V_(cell)) is measured and when it drops to about3 to 30% of V_(c) (preferably 10 to 15% of v_(c)) the coloring voltageV_(c) is re-applied. Schematically an electric circuit showing V_(cell)and V_(c) (or V_(B)) is shown in FIG. 45.

[0367] In addition to varying t₁ and t₂ with temperature, the coloringand bleaching voltages may also be varied with temperature if desired.For example, depending on the devices, higher voltages may be used atlower temperature or vice-versa. Additionally, with temperature feedbackto the control circuities, both the duration (i.e., t₁ and t₂) and thevoltage can be varied simultaneously to further mitigate electrical orelectrochemical stress on the EC cell.

[0368] The voltage can be made temperature dependent by having athermistor-containing voltage reference in the power supply. Thisthermistor can be a NTC (negative thermal coefficient) or a PTC(positive thermal coefficient) type. As the temperature rises theresistance will be lower in NTC thermistors. Consequently, whenincorporated with suitably-biased series resistors and an operationalamplifier (op amp), the reference voltage to the error-sensing op ampwill be lower as temperature increases, resulting in a lower voltageapplied to the EC cell at higher temperatures.

[0369] An example of a circuit incorporating an NTC thermistor TM1 andan op amp OP1 is shown in FIG. 39. As the temperature increases, theresistance of the TM1 will be lower, resulting in a reference voltagefrom PS2 to OP1 to be lower. Thus, output voltage V_(OUT) will be lower.Accordingly, a properly designed resistor stack with a combination ofseries and/or parallel resistors incorporating such thermistors wouldcause the voltage needed (V_(OUT)) to track with operating temperature.In a particular example, the values of each component were: PS1 was 12VDC, R1 and R2 were 10K Ω each, C1 was 10 μF, PS2 was 2.5 VDC, OP1 was aLM324 op amp available from National Semiconductor, Santa Clara, Calif.,TM1 was an NTC Thermistor having a resistance of 1.76 kg at 50° C., andthe output voltage was 1.35 V.

[0370] A PTC thermistor TM2 can also be used in a circuit to change theoutput voltage with temperature, an example of which is shown in FIG.40. In a particular example, the values of each component were similarto that example above, PS3 was 12 VDC, R3 and R4 were 10K Ω each, C2 was10 μF, PS4 was 2.5 VDC, OP2 was a LM324 op amp, TM1 was an PTCThermistor having a resistance of 1.76k Ω at 5° C. , and the outputvoltage was 1.15 volts.

[0371] Additionally, the thermistor can also be used in a comparatorcircuit to trigger the microprocessor to use different t₁, and t₂periods, for example, as shown in FIG. 41. In the example, thethermistor TM3 used was a NTC Digikey part # PNT 117-ND available fromPanasonic, Cupertino, Calif., with a resistance of 1.76K Ω at 50° C. Thepotentiometer resistor R5 in series with the thermistor was adjusted tomatch the thermistor's set value, i.e. 1.76K Ω. PS5 was 12 VDC, R6 andR7 were each 15K Ω, and the op amp was an LM324 op amp available fromNational Semiconductor. As a result, the voltage drop across R6 and R7(Vcc) is 5.0 V. The positive input of the op amp is fixed at 2.5 V bythe two 15K Ω series resistors R6 and R7. At temperatures lower than 50°C., the TM3 resistance is higher than 1.76K Ω resulting in a voltage ofhigher than ½ of Vcc (that is, 2.5 V) to the negative input of the LM324op amp. Since the negative input is higher than the positive input thereis no output from the op amp at such lower temperatures. When thetemperature climbs to 50° C. and above, the resistance in the thermistordrops below 1.76K Ω, thereby lowering the voltage below 2.5 V andresulting in a positive output signal from the op amp that can be routedto a microprocessor input port. The microprocessor can then change thet₁, and t₂ periods in response to the positive output signal.

[0372] Based on this circuit, the output of the op amp will be turned onat the threshold temperature; however near the region of this thresholdthere may be thermal fluctuations which may cause the output toerratically turn on and off. In order to eliminate such erraticbehavior, a positive hysteresis can be added to the op amp comparatorusing positive feedback. As shown in FIG. 42, a feedback loop can beformed by resistor R12, resulting in a Schmitt trigger. In the example,the values of the components were those of the corresponding componentsin FIG. 41, with the added resistors R11 being 10K Ω and R12 being 1K Ω.

[0373] With such a Schmitt trigger in the circuit, the low triggerthreshold is different from the high trigger threshold (the differencebeing the hysteresis intentionally induced in the comparator, ratherthan a single threshold value as in a conventional comparator). SuchSchmitt triggers can also be used in photosensors to detect daylight—itis well known that around the region of daylight threshold, e.g., duringdusk and dawn, photocells can behave erratically. Having positivehysteresis in the op amp comparator will aid in obtaining a smoothoutput. Furthermore, Schmitt triggers can be used in EC skylightcircuits where both photosensors and temperature sensors are employed.

[0374]FIG. 43 shows an example of an implementation of an adjustablevoltage power supply where the output voltage supplied to theelectrochromic panel ECU1 can be tuned to give two different outputvoltages depending on the transistor switch T4 which will be activatedwhen there is a predefined temperature change. In a particular example,PS7 was 12 VDC, PS8 was 2.5 VDC, R14 and R13 were each 10K Ω, R15 andR16 were each 1K Ω, R17 was 4K Ω, and C3 was 10 μF. The transistors T3and T4, and the op amp were those described above. The trigger to thebase of T4 can come from either a microprocessor port as shown in FIG.43, or the comparator output from a circuit as shown in FIG. 41 or 42.Upon turning on of transistor T4, the resistor R15 will be in parallelwith the reference resistor R14 resulting in a lower overall resistanceand hence lower reference voltage to the error-sensing op amp. Theoutput voltage will also be lower. Alternatively, such output voltagecan change to vary the EC color voltage below full coloration, e.g.,during half color.

[0375] The EC power supply can also incorporate current limitation,e.g., using simple transistor switching or current holdback techniques.The addition of a sensing resistor in series with the power output,together with another transistor as shown in FIG. 44, can limit themaximum current flowing in the circuit by the judicious choice of thesensing resistor R20 value. This sensing resistor can be fixed forconstant maximum current or made variable for variable current limitingin the circuit. In a particular example, PS9 was 12 VDC, PS10 was 2.5VDC, R18 and R19 were 10K Ω, TM4 was an NTC thermistor having aresistance of 1.76K Ω at 50° C., Op Amp OP6 was an LM324, T5 and T6 were2N3904 transistors described above, and C4 was 10 μF. With sensingresistor R20 having a resistance of 1K Ω (V_(BE) of T6 is 0.7 volts),the voltage output V_(OUT) was 1.35 volts, and was limited to a currentI_(OUT) of 0.7 mA.

[0376] A particular benefit of this current limiting is in the case ofan electrical short—the circuit will allow only the maximum limitedcurrent to flow through rather than a potentially damaging high current,thus offering protection.

[0377] In some devices, the variation in t₁ may be much more stronglydependent on temperature than t₂ (e.g., see device #1 and 2 in Table 5below). In such cases the powering circuit could be simplified so thatonly t₁ varies with temperature and t₂ is fixed in duration.

[0378] In all the examples above it is assumed that the coloration andbleaching are controlled by applying a pre-specified maximum potentialand that this potential can be a step, ramp, non-linear, etc. In anothermethod the power supply can be configured so that it applies apre-specified current for coloring and bleaching, subject to a maximumsafe-potential. This means that the applied potential from the powersupply will vary with time (to compensate for changes in impedance, forexample).

[0379] In coloration, as an example, a controlled current source couldbe used. The current is reduced, or the current source is removed, asthe maximum safe-potential is reached. Thus, when a pre-specifiedpotential between the cell electrodes is reached, the power source isremoved. A current limit for coloring (or bleaching) for non-internalbusbar cells is typically chosen between 50 to 5000 μA/cm² of activearea of the EC cell, more preferably between 100 and 1000 μA/cm². Forcells with internal busbars current limit (if imposed) can exceed theupper limit of this range to insure that time to color and bleach israpid.

[0380] In all cases where the temperature is being measured, it isimportant that the temperature measuring or sensing elements such asthermistors, ferroelectric capacitors, thermocouples, or other suchtemperature measuring means, are mounted in such a way that they senseor measure temperatures that are similar to the temperature of the ECcells. That is, the measured temperature must have a correspondingrelation to the temperature of the EC cell. For example, the measuringmeans could be mounted on a cell surface, on a cell edge, or at aposition proximate to the cell so that the temperature of the cell andthe temperature of the sensing element are similar. In some cases it maybe preferred to mount the thermistor so that it is hidden from thedirect view of the user. Adhesives with high thermal conductivity may beused for mounting so that the sensing elements are close in temperaturesto the substrates they are mounted on.

[0381] In other examples where the EC cell is large, or where thesensing element controls multiple EC cells, it is apparent that thesensing element should measure a temperature that is relevant to thetemperature of the large EC cell or of the multiple EC cells. Suchrelevant temperature would be, for example, an average temperatureacross the large EC cell or the multiple EC cells. In other cases, thepeak or low temperature might be relevant. Accordingly, the sensingelement should be positioned so that such a relevant temperature issensed or measured.

[0382] The above descriptions of determining t₂ may also be used fordetermining and/or controlling t₁. The time period t_(b) may be fixed orcould be varied.

[0383] The Examples which follow are intended as an illustration ofcertain preferred embodiments of the invention, and no limitation of theinvention is implied.

Example 16 With Thermistor and/or Ferroelectric Capacitor

[0384] Referring to FIG. 36A, the EC control circuit was designed toincorporate the intermittent powering of the EC cell E1, as describedabove. In this example, the coloring and bleach potentials were fixed at1.2 V and −0.3 V respectively, while t₁ and t₂ were allowed to vary withtemperature.

[0385] The system can utilize any convenient voltage as would beapparent to one of ordinary skill in the art. In this case, for example,12 V DC is used. The voltage can be supplied from any convenient sourcesuch as, for example, from a car battery or from a transformer thatsteps down 110 V AC to 12 V DC. The circuit uses a LM 556 dual timer(National Semiconductor, Santa Clara, Calif.), which includes an astabletimer U1/A and a monostable single shot timer U1/B, to control the timedcycles for the EC device.

[0386] Astable timer U1/A includes an RC circuit comprised of resistorsR2, R3, and capacitor C1. This astable timer provides the holding andvoltage application periods. The periods for t₁ and t₂ are obtained byusing the formula t₁=0.693(R3+R2)C1 and t₂=0.693(R2)C1. The output oftimer U1/A drives a transistor Q1 which then further drives a transistorQ2. Transistor Q2 activates the relay K1:A which upon closing appliesthe coloring potential from the 1.2 V voltage source.

[0387] A pair of diodes D1 and D2 isolate the outputs of U1/A and U1/Bfrom each other. Astable timer U1/A is cycling constantly but its outputis only applied to electrochromic cell E1 when switch S3 is in the colorposition after an initial time period, for example, 200 sec from U1/B.

[0388] Resistors R2 and R3 may each be replaced with a NTC thermistors,e.g., model DC95-& 104Z available from Thermometrics, Edison, N.J., toallow for t₁ and t₂ compensation at electrochromic cell E1. For example,the cycling conditions of a particular EC device at 25° C. are t₁=138sec, t₂=69 sec. These times are obtained with thermistor R2 and R3values of 100K Ω and C1 of 1 mF. Using the thermistors described, theresistance increases to 1 M Ω at −25° C. and decreases to 23K Ω at 65°C., resulting in t₁=1444 sec and t₂=722 sec at −25° C., and t₁=32 secand t₂=16 sec at 65° C., respectively.

[0389] Monostable single shot timer U1/B provides the initialduration—in this case, for example, 200 sec, of coloring or bleachingpotential. The duration for the initial color (t₁) or bleach (t_(b)) iscalculated according to the formula t=R3*C4. The values are calculated,in this example, to yield the 200 sec duration to initially color orbleach the cell and is triggered by switch S1. The output from switch S1drives transistors Q2 and Q3. Resistor R6 can be replaced with an NTCthermistor to obtain longer and shorter initial bleaching (or coloring)periods, respectively.

[0390] The potential which is applied to electrochromic cell E1 dependson the position of switch S3, which the user selects. If switch S3 is inthe coloring position, astable timer U1/A takes over after the initial200 sec coloring cycle and then electrochromic cell E1 is cycledintermittently by astable timer U1/A to maintain coloration. Astabletimer U1/A is never applied while switch S3 is in the bleachingposition.

[0391] Alternatively, ferroelectric-capacitors having a Curie point,T_(c), for example, below −45° C., based on SrTiO₃— containingcompositions, can also be used in the timer circuit to providetemperature sensitive capacitors. In these capacitors, the capacitancedeclines with increasing temperature. Accordingly, such capacitors canbe used to cause the periods of t₁ and t₂ to be changed alongnon-linearly with temperature changes, such as to cause even longerperiods at lower temperatures and shorter periods at highertemperatures. Furthermore, a combination of thermistors andferroelectric capacitors can be used simultaneously to obtain the RCproduct necessary to change t₁ and t₂ according to temperature.

[0392] A microcontroller can also be used to obtain t₁ and t₂functionalities in the control circuities using built-in timer modesthus negating the use of any external timer chips such as LM555 orLM556. Examples of such microcontrollers are PIC16F84 from Microchip(Chandler, Ariz.), MC68HC11E9 from Motorola (Tempe, Ariz.), and Z-80from Zilog (Campbell, Calif.). Temperature sensors can be connected tothe microcontroller to change t₁ and t₂ accordingly. Flash memory orEEPROM can further be utilized in conjunction with the microcontrollerto store information on the temperature dependence, electrical historyand aging properties of the EC cell. This information will then be usedas feedback to optimize the cell bleaching and coloring characteristics.These may include changes to V_(c), V_(b), T_(cl)%, T_(c2)%, t₁, t₁, t₂and t_(b).

[0393] In a particular example, a Microchip microcontroller PIC16F84 asshown in FIG. 36B was used (in place of the LM556 dual timers of FIG.36A) in a circuit similar to that shown in FIG. 36A. The EC cell wasconfigured so that it could only be colored during the day time by usinga CdS photocell sensor to determine whether it is daytime or nighttime.At night, the EC coloring function was disabled. Upon coloring, acoloring potential of 1.2 V from the power supply would be applied tothe cell for 3 minutes. Following this initial coloring potential, thespecific t₁ and t₂ intermittence functionality (for example, 45 sec turnoff and 15 sec turn on of the coloring potential) was also written intothe program. Upon bleaching, a −0.3 V would be applied to the cell for 3minutes. During the coloring or bleaching process, the output pin wouldbe enabled turning on the relay or semiconductor switches to power theEC cell directly from the coloring or bleaching power supplies. Thefirmware was programmed into the microcontroller using a PicStart PlusProgrammer. A thermistor suitably mounted on the EC cell can also beconnected to one of the I/O ports in the P1C16F84. The change inresistance of the thermistor is then correlated to temperature of the ECcell. Depending on the temperature measured, the coloring and bleachingpotentials, t₁ and t₂ characteristics can then be controlled.Microcontrollers can also be used to control the powering method of theEC cells during coloring and bleaching. This includes specific potentialramps, constant current control, or potential increases and decreases inmultiple discrete steps.

Example 17 Change in t₁ and t₂ With Temperature of ElectrochromicDevices

[0394] Various electrochromic devices, 3 in×3 in, were fabricated using12 ohms/square ITO as the conductive substrates. The tungsten oxidecoating deposition methods and device fabrication processes used inthese EC devices were similar to the methods and processes described incopending U.S. patent application Ser. No. 09/155,601 (incorporated byreference herein) which also describes the use of and methods tofabricate Selective Ion Transport Layers (SITL). The EC devices weremade both with SITL layers and without SITL layers. The electrolyteconsisted of at least one solvent, one dissociable salt and at least oneredox promoter. Polymeric viscosity modifiers and UV stabilizers andwater were also added.

[0395] Although any of the solvents described in copending U.S. patentapplication Ser. No. 09/155,601, could be used, although carbonates,sulfolanes, glymes, and their mixtures are preferred. Examples ofsuitable carbonates are propylene carbonate, ethylene carbonate, ethylpropyl carbonate, isopropyl ethyl carbonate, diethyl carbonate, methylpropyl carbonate, isopropyl methyl carbonate, ethyl methyl carbonate,dimethyl carbonate, butylene carbonate and other alkyl carbonates.Examples of some other suitable solvents are alkyl sulfones, tetraglyme,toluene, xylene, decaline and other aliphatic and aromatic alkyls withor without substituted polar groups.

[0396] Dissociable salts were typically based on alkali metal cations,such as lithium, sodium, and potassium. Some examples of suitable anionsare perchlorate, tetrafluoroborate, triflate, etc., as described incopending U.S. patent application Ser. No. 09/155,601, which lists othersuitable salts.

[0397] When tungsten oxide, molybdenum oxide and other cathodic oxidesand their mixtures were used as chromogenic layers, the redox promotersused in the devices were typically based on ferrocene and itsderivatives. Substituted ferrocenes with electron donating groupsattached on the cyclopentadiene rings of the ferrocenes are a preferredsub-class in ferrocenes. These groups can be substituted to any of thecyclopentadiene rings. Further, the substituted groups may be the sameor different on each of the rings. Such groups include methyl, propyl,n-butyl, tertiary butyl, etc. Examples of such ferrocenes includedecamethyl ferrocene, octamethyl ferrocene, tertiary butyl ferrocene,interannual substituted ferrocenes such as 1-1′-(propane-1,3-diyl)ferrocene, 1,1′:3,3′-bis(propane-1,3-diyl) ferrocene,1,1′:2,2′:4,4′-tri(propane-1,3-diyl) ferrocene. Another preferredsub-class of ferrocenes are biferrocenes and bridge ferrocenes, where inthe latter, the cyclopentadiene rings of different ferrocene moleculesare chemically bonded to each other. Examples of these include2,2-bis(tert-butylferrocenyl)propane, 2,2-bis(ethyl ferrocenyl)propane,etc. Further, the selection of the ferrocene will also influence theextent of the back reaction with other ingredients, components anddevice construction details remaining the same.

[0398] Typically, inclusion of polymers that are soluble in theelectrolyte will result in increased viscosity and accordingly suchpolymers can be used as viscosity modifiers.

[0399] The size of such crystals should typically be smaller than about0.5 μm, preferably less than 0.2 μm so that they do not create hazinessin optically clear systems. Some preferred polymers are polymethylmethacrylate, polyvinyl chloride, polyvinyl chloride and polyvinylacetate copolymers, polyvinyl butyral, polyacrylonitrile and itscopolymers, polyvinylidene fluoride, copolymers of polyvinylidenefluoride and hexafluoropropylene. The last two are available from ElfAtochem North American (Philadelphia, Pa.) under the trade names ofKynar and Kynar flex respectively.

[0400] In one of the samples the electrolyte was processed using asol-gel technique to form a solid. The solid resulted from the formationof “Si—O—Si” cross-linkages in-situ after filling the EC cell with aelectrolyte precursor. This is also described below.

[0401] The selection and the concentration of the ingredients describedabove will influence the extent of the back reaction while othercomponents and device construction details remain the same. The backreaction will change with temperature and this will cause change in t₁and t₂.

[0402] As shown in Table 5 below, the presence and absence of a SITLlayer, the type of SITL layer, and any changes in the electrolyte haveconsiderable influence on t₁ and t₂. Polyceram SITL layer formation bysol-gel processing is described below. Polystyrene-sodium-sulfonate(PSSNa) SITL layer was processed by dip-coating the tungsten oxidecoated substrates with a 540,000 mol. wt. PSSNa solution (5% byweight/vol) in a 50/50 mixture (by volume) of distilled water andreagent grade ethanol and 0.01% of a surfactant, Triton X-100 availablefrom Aldrich Chemical Co. (Milwaukee, Wis.).

[0403] The devices were colored by applying 1.2 V. The values of T_(c1)%and T_(c2)% (FIG. 35) were 10% and 15% respectively. The leakage currentwas measured as the current consumed after applying the coloringpotential for 15 minutes. The table also shows that when ferrocene hasbulky constituents, such as in the compound 2,2-bis(ethylferrocyl)propane, a lower leakage current is obtained. For example,compare the leakage current of device 1 to that of device 2, and theleakage current of device 5 to that of device 6.

[0404] The various electrolyte compositions were:

[0405] electrolyte A: 85% Propylene carbonate, 0.8% 2,2-bis(ethylferrocenyl)propane, 0.4% LiClO₄, 9.4% PMMA, 3.6% UV400, and 0.1% water(all percenntages by weight).

[0406] Elecrolyte B: 85.2% Propylene carboate, 0.7% ferrocene, 0.4%LiClO₄, 9.5% PMMA, 3.6% UV400 and 0.7% water (all percentages byweight).

[0407] Electrolyte C: 53.6% Propylene Carbonate, 35.7% Sulfolane, 8.4%Poly(methy methacrylate), 1.0% Deionized water, 0.8% Ferrocene, 0.5%Lithium perchlorate (all percentages by weight). TABLE 5 De- Type ofLeakage vice Electrolyte SITL SITL Temp. t₂ current # composition Layerlayer ° C. t₁ (s) (s) (μA/cm²) 1 Electrolyte C No 25 30 20 210 50 20 20370 70 15 20 530 2 Electrolyte A No 25 61 6 126 50 31 4 268 70 24 4 3923 See forma- No 25^(a) 7 31 29 tion of sol- gel electro- lyte below thistable 50^(b) 5 15 87 70^(c) 2 12 151 4 Electrolyte B Yes Poly- 25 107914.4 6.4 ceram-2 50 431 7.2 31.5 70 184 5.8 90.0 5 Electrolyte B YesPoly- 25 590 24 10 ceram-1 50 145 8 47 70 64 6 136 6 Electrolyte A YesPoly- 25 2749 10.2 4.8 ceram-1 50 1272 6 13 70 785 4 26.7 7 ElectrolyteC Yes PSSNa 25 3600 25 3.3 70 900 7 14.5

[0408] Example: Formation and processing of Polyceram-1 SITL Layer(CH₃(OCH₂CH₂)_(n)OCONH(CH₂)₃Si(OC₂H₅)₃/Si(OCH₃)₄, overcoated on WO₃electrode)

[0409] Polyceram layer was processed as described in the examples givenbelow. Polyceram layer was made in the same way but the ratio ofingredients was modified. The weight ratio of(CH₃(OCH₂CH₂)_(n)OCONH(CH₂)₃Si(OC₂H₅)₃ to Si(OCH₃)₄ was 1:0.51 in thecase of Polyceram-1 but 1:1.02 in the case of Polyceram-2.

[0410] 75.00 g of poly(ethylene glycol) methyl ether, CH₃(OCH₂CH₂)_(n)OH(number average MW=ca. 350, obtained from Aldrich Chemical Co.,Milwaukee, Wis.), 58.31 g of 3-(triethoxysilyl) propylisocyanate,(C₂H₅O)₃Si(CH₂)₃NCO, and 0.15 ml of dibutyltin dilaurate were heated atapproximately 50° C. under nitrogen, with stirring, for 2 hrs to give asilylated derivative with the nominal formula:CH₃(OCH₂CH₂)_(n)OCONH(CH₂)₃Si(OC₂H₅)3.

[0411] 24.30 g of CH₃(OCH₂CH₂)_(n)OCONH(CH₂)₃Si(OC₂H₅)₃, 49.59 g ofC₂H₅OH and 2.20 g of H₂O (acidified to 0.15 M HCl) were combined andrefluxed for 30 mins. The solution was then cooled and 12.38 g ofSi(OCH₃)₄ added and the resulting solution refluxed for 60 mins. Thesolution was then cooled and 5.86 g of H₂O (acidified to 0.15 M HCl) wasadded and the resulting solution refluxed for 60 mins. The solution wasthen cooled and 3.00 g of Amberlyst® A-21 ion-exchange resin (Rohm &Haas Co.) added, followed by gentle stirring. After 30 mins the solutionwas filtered through a fritted glass disc Buchner funnel. 45.00 g of thefiltrate was taken and 0.21 g of 3-aminopropyltriethoxysilane was added.The resulting solution was diluted 1:1 (by weight) with ethanol andfiltered through a 1 μm syringe filter. It was then spin-coated on atransparent WO₃ ITO coated glass substrate. The coating was cured at135° C. for 1 hr under humid atmosphere, after this treatment it has athickness of about 0.6 μm . A device was then assembled as described inComparative Example 1.

[0412] Example: Formation and processing of Polyceram-2 SITL layer(CH₃(OCH₂CH₂)_(n)OCONH(CH₂)₃Si(OC₂H₅)₃/Si(OCH3)₄ overcoated on WO₃electrode)

[0413] 6.08 g of (CH₃(OCH₂CH₂)_(n)OCONH(CH₂)₃Si(OC₂H₅)₃, 12.40 g ofC₂H₅OH and 0.55 g of H₂O (acidified to 0.15 M HCl) were combined andrefluxed for 30 mins. The solution was then cooled and 6.19 g ofSi(OCH₃)₄ added and the resulting solution refluxed for 60 mins. Thesolution was then cooled and 2.93 g of H₂O (acidified to 0.15 M HCl) wasadded and the resulting solution refluxed for 60 mins. the solution wasthen cooled and 1.30 g of Amberlyst® A-21 ion-exchange resin (Rohm &Haas Co.) added, followed by gentle stirring. After 30 mins the solutionwas filtered through a fritted glass disc Buchner funnel. The filtratewas diluted 1:2 (by weight) with ethanol and filtered through a 1 μmsyringe filter. It was then spin-coated on a transparent WO₃ ITO coatedglass substrate. The coating was cured at 135° C. for 1 hr under a humidatmosphere, after this treatment it had a thickness of 0.3 μm. A devicewas then assembled as described in Comparative Example 1.

[0414] Example: Formation of sol-gel electrolyte

[0415] This describes a crosslinkable electrolyte which can besubstituted for the electrolyte in cells such as those given inComparative Example 1a or in other examples with SITL overlayersdescribed earlier. The electrolyte was prepared in the following way:12.00 g of poly(ethylene glycol). HO(CH₂CH₂O)_(n)OH (number averagemolecular weight=ca. 400, obtained from Aldrich Chemical Company), 15.58g of 3-(triethoxysilyl) propyl isocyanate, (C₂H₅O)₃Si (CH₂)₃NCO(obtained from Aldrich Chemical Company), and 0.03 g dibutyltindilaurate, (CH₃(CH₂)₃)₂Sn(O₂C(CH₂)₁₀CH₃)₂, were heated to approximately70° C. under nitrogen, with stirring, for 15 minutes to yield asilylated derivative with the nominal formula: (H₅C₂O)₃S1(CH₂)₃HNOC(OCH₂CH₂)_(n)OCONH(CH₂)₃Si (OC₂H₅)₃.

[0416] 2 g of CH₃ (OCH₂CH₂)_(n)OCONH(CH₂)₃Si (OC₂H₅)₃, 1.50 g(H₅C₂O)₃Si(CH₂)₃HNOC (OCH₂CH₂)_(n)OCONH(CH₂)₃Si(OC₂H₅)₃ (prepared asabove), 1.75 g γ-butyrolactone, 0.0326 g ferrocene, and 0.4107 g LiClO₄are stirred until a clear solution is formed. Then 0.3636 g H₂O(acidified to 0.15 M HCl) is added. The solution is stirred untilhomogeneous. A cell fabricated as in comparative Example 1 utilizing anITO electrode and a transparent WO₃ ITO coated glass substrate is thenfilled with the solution obtained above. The cell thickness in thisexample was 53 μm rather than 210 μm as given in the earlier example.After filling the cell, the solution forms a rigid gel (net work) within10 hours. The gel time can be controlled, e.g., by changing the type andamount of catalyst (e.g., HCl is used above) as known in the art,temperature of cell after filling and using appropriate functionality ofthe ingredients. Functionalised ferrocenes also could be used which willattached chemically to the electrolyte network. Some exemplaryferrocenes are:

[0417] These ferrocenes could be used by themselves or in conjunctionwith non-functionalized ferrocenes (the ones which will not chemicallyattach to the network). Depending on the cell characteristics ifnon-ferrocene redox materials are used, the same can be implemented fornon-ferrocene redox materials. The cell may also consist of ferroceneand non-ferrocene based redox materials.

[0418] Power consumption reduction in EC devices by using switchingpower supplies:

[0419] The power consumption of these devices can be further reduced byincorporating such elements in the circuit that would efficiently stepdown the voltages from the incoming power supply to the desiredcoloration or bleaching voltages. For example, a typical car battery hasan output of about 12 V, while an EC device might only need 1 to 2 voltsfor coloration, for example 1.2 V. Thus, if the EC device needs acurrent of 10 mA in the colored state at a voltage of 1.2 V, then apower conserving circuit would allow only a 1 mA drainage from thebattery at 12 V assuming that the power is converted at 100% efficiency.

[0420] Typical power supplies for powering EC devices in automotivemirrors use linear regulators or linear regulation for the voltageconversion process. Although widely used for such applications, thepower conversion efficiencies of linear regulators are usually very low,typically 10-30%. The conversion efficiency, however, is typically not amajor concern. Since the EC mirror is normally operated when the car inturned on, the current or power draw is not a significant drain on thecar's alternator and linear regulation can be utilized. Examples of suchcircuits are described in U.S. Pat. Nos. 5,148,014, 5,193,029, and5,220,317, each incorporated herein by reference.

[0421] However, the switching regulator can be used for EC devices astaught in the present invention and can offer up to 95% efficiency. Inthe prior art power supplies, the current draw is usually maintainedwhen the voltage is switched from high to low potential. For example,for linear regulators, in going from 12 V at 1 mA, to 1.2 volts, theoutput current will still be 1 mA, which reflects a power conversionefficiency of only 10%. In this invention, use of circuits thatregulates the power supply voltage by a switching function to controlthe electrochromic products increases the power conversion efficiency byat least two fold over linearly regulated power supplies.

[0422] In aircraft, boats, eyewear and automotive EC windows, such asautomotive EC sunroofs, where the coloration needs to be maintained evenwhen the vehicle is in a mode such as when parked, where the engine isoff, the current drain from the battery becomes a critical issue. Incars, the current draw is usually preferably 2 mA or less at 12 V inorder not to drain the battery excessively. During this colorationstate, the present invention subjects the cell to an intermittentvoltage rather than a continuous voltage, thereby enhancing devicedurability. During initial coloration and intermittent colorationperiods (t₂) the switching power supply of the present invention is usedto convert the power efficiently to reduce the battery drain. During theholding period when no current is flowing, the regulator shouldpreferably have a low or no quiescent current.

[0423] An example of a switching regulator circuit used in thisinvention is shown in FIG. 37A. The circuit is able to regulate even lowvoltages below about 1.2 V. As described earlier, the switchingregulator circuit of this invention has a low or no quiescent current inorder not to drain the battery excessively. Switching regulators, asused here, have lower current drains than linear regulators. Theswitching regulator of the present invention preferably should have aquiescent current drain of lower than 100 mA. It is more preferred thatthe switching regulator of the present invention have a quiescentcurrent drain of lower than 25 mA and most preferably lower than 5 mA.Such low current drains minimize drawdown of the battery in situationswhere the battery is not being charged such as while the vehicle isparked with ignition off.

[0424] Comparative Example: Linear Regulator

[0425] During operation of a prior art well known linear regulator suchas, for example, National LM317 (National Semiconductor, Santa Clara,Calif.) series pass transistor is turned on continuously and the outputvoltage is determined through a voltage divider and a feedback circuit.There is a significant heat dissipation load for the transistor.Furthermore, as a result of the continuous “on” state of the transistor,there is a constant background current draw regardless of the load. Whena load is connected, the conversion efficiency is typically not morethan 30% for a ten fold change in voltage down conversion.

[0426] Example of Switching Regulator

[0427] In a switching regulator (e.g. National LM78S40), pulse widthmodulation (PWM) is used to switch the input voltage through a highspeed transistor at an adjustable duty cycle. In contrast to a linearregulator where the series pass transistor is always on, in a switchingregulator the series pass transistor is turned on and off at aconvenient predetermined frequency (usually in the range of about 25-250kHz). The output voltage is the average of the rectangular pulsesresulting from such switching. Switching regulation results in higherefficiency, such as over 30% and can be as high as about 95%. Inaddition, the quiescent current draw is also very low, typically lessthan imA thus keeping overall heat dissipation low. Additionally in someswitching regulators, e.g., Maxim MAX 1627 (Maxim Company, Sunnyvale,Calif.), the quiescent current draw can be further lowered to 1 μA.

[0428] As shown in FIG. 37A, a switching regulator circuit used in thisinvention can be based on a National LM78S40 switching regulator chipU1. It accepts a 12 V pre-regulated input voltage. A peak current of 1.5A is assumed for this regulator. A sense resistor calculated as0.33/peak current according to the manufacturer, R4 detects the peakincoming current. Based on the value of input and output voltageexpected, a duty cycle of 23% is obtained. Assuming a switchingfrequency of 25 kHz, a turn-on time of 33 μs is calculated. Based on theturn off time, the timing capacitor C2 of 0.15 μF is then used to setthe switching frequency to 25 kHz. An inductor, L1 was used to couplethe switching pulses while the capacitor C1 reduces the ripples in thepulses to an average voltage output. The combination of peak current andturn-on time results in an inductance of 50 μH. Voltage ripple of 1% istolerated resulting in the capacitor C1 of about 1mF. The chip containsa built-in PWM module, Darlington series pass transistor and referencevoltage. Trimmer resistor, R5, in conjunction with series resistor R3,then sets the output voltage. The built-in reference voltage is set at1.3 V which is the lower limit for the regulated voltage. In the circuitthe reference voltage is reduced by using a voltage divider via seriesresistors, R1 and R2 of 1 M Ω each to further lower the minimum voltageregulated to 0.65 V.

[0429] To change the applied potential to an EC device with temperature,an NTC thermistor can also be used in place of trimmer resistor R5. Athigher temperatures, the resistance decreases, leading to lower coloringand bleaching voltages while at lower temperatures, the resistance ishigher resulting in higher voltages.

[0430] Switching regulator radiates EMI due to the switching transistor.Adequate shielding, e.g. Faradaic shield, must be provided to mitigatesuch EMI to reduce electromagnetic interference with other subsystemsincluding communications such as a cellular phone. For example theshielding aspect could be useful for powering of EC components in a caror any other transportation vehicle. It is also novel to use switchingand linear regulator with the former working when the car is in a parkedstate while the latter being used while the car is parked (ignitionoff), the degree of interference to other electronic systems is lower.

[0431] Example of a Switching Regulator With Ultra Low QuiescentSwitching Current

[0432] A switching regulator used in this invention employing a MAXIMMax 1627 yielding very low quiescent current of 0.001 mA is shown inFIG. 37C. The switching efficiency is a high as 85% at 1 A current draw.Without modification using the manufacturers' specification, this chipoutputs voltage at a lower limit of 1.27 V. In this particular example,the circuit is modified, to allow output voltages lower than 1.27 V, byhaving feedback resistors R2 and R1 connected through a high speedcomparator MAXIM Max 987. The p-MOSFET used in the circuit wasInternational Rectifier (El Segundo, Calif.) IRF7416.

[0433] Example of Ramped Voltage Application

[0434] The voltage applied to the EC cell may consist of a non-linearramp. The ramp only refers to the time period when the voltage ischanging before the voltage settles at the hold potential (e.g., V_(c)isholding potential in FIG. 38B). Such non-linearity can be obtained,e.g., by having some amount of internal resistance in the power supply.This internal resistance can be intentionally designed into the powersupply itself or by inserting an external resistor between the voltageterminal and the EC cell. This is shown in FIG. 38A where resistor R7 isplaced in series with the power supply output and EC cell. FIG. 38Cdescribes the various shapes that the voltage vs. time curves can followdepending on the circuit parameters. The applied voltage is across theEC cell and the resistor. During bleaching or coloring times, there willbe a large initial surge of current resulting in a sizable ohmic drop inR7 which then limits the voltage applied to the EC cell. At saturation,only a very low amount of current flows, and the voltage drop across R7becomes negligible and hence the EC cell sees the full potential again.The overall voltage applied to the EC cell during coloring and bleachingprocesses appears similar to a capacitor charging curve. The sharpnessof the curves depends on the value of resistor used; larger resistanceresults in more gradual and slower saturation.

[0435] Switching Power Supply Where Output Voltage Varies WithTemperature

[0436] A switching regulator circuit was constructed similar to the onedescribed previously except that a thermistor was located in place offixed resistor R5-see FIG. 37B. An example of the thermistor used is KED331BZ from Thermometrics (Edison, N.J.). It exhibits resistance valuesof 4000 Ω and 60 Ωat −25° C. and 65° C. respectively. By having anotherfixed resistor R6 with a value of 3.6 kg in series with thermistor R5and fixed resistor R3 with a value of 5.6 k Ω, the voltage wasautomatically tuned to 1.3 V and 1 V at −25° C. and 65° C. respectively.

[0437] Other variations and modifications of this invention will beobvious to those skilled in the art. This invention is not limitedexcept as set forth in the following claims.

What is claimed is:
 1. An edge busbar having a shape effective to beperipherally disposed about a substantial perimeter of an edge, betweena first surface and an opposite second surface, of an electrical device,wherein said edge busbar comprises: at least one electrically conductiveconnector portion effective to form an electrically conductive path fromsaid first surface, wrapping transversely around a portion of said edge,to said opposite second surface; and an electrically conductiveperimeter portion in electrical contact with said connector portion,wherein said perimeter portion is peripherally on said substantialperimeter.
 2. An edge busbar according to claim 1, wherein saidconnector portion includes a plurality of said electrically conductivepaths; and wherein said perimeter portion is in electrical contact withsaid plurality of electrically conductive paths.
 3. An edge busbaraccording to claim 1, further including a conductive layer formed onsaid first surface; and wherein said connector portion has at least oneseparating portion electrically bridged by said conductive layer.
 4. Anedge busbar according to claim 1, wherein said connector portion andsaid perimeter portion are composed of aluminum, copper, gold, silver,tungsten, stainless steel, tin, copper/beryllium alloy, indium, nickel,rhodium, nichrome, solder, or a conductive metal oxide.
 5. An edgebusbar according to claim 1, wherein said edge busbar is composed of ametal in substantially a sheet configuration, wherein said sheetincludes a ribbon having a plurality of first finger portions extendingfrom a side of said ribbon, said ribbon forming said perimeter portionand said first finger portions forming said connector portions.
 6. Anedge busbar according to claim 5, wherein said sheet further includes asecond plurality of finger portions extending from an opposite secondside of said ribbon, said ribbon forming said perimeter portion and saidfirst and second finger portions forming said connector portions.
 7. Anedge busbar according to claim 1, wherein said at least one connectorportion is made from a cured metallic frit, conductive ink, orconductive adhesive.
 8. An edge busbar according to claim 1, whereinsaid at least one connector portion is composed of indium tin oxide ordoped tin oxide.
 9. An edge busbar pair comprising a first edge busbarand a second edge busbar, each edge busbar of said pair having a shapeto be peripherally disposed about a respective substantial perimeteredge of a first substrate and a second substrate respectively of anelectrical device, said edge busbar pair further including: said firstbusbar comprising a first connector portion and a first perimeterportion, said first connector portion effective to form an electricallyconductive first path from a first front surface of said firstsubstrate, wrapping around a portion of said edge of said firstsubstrate, to an opposite first back surface of said first substrate,said first perimeter portion being in electrical contact with said firstconnector portion, and wherein said first perimeter portion isperipherally on said first substantial perimeter of said firstsubstrate; a second busbar comprising a second connector portion and asecond perimeter portion, said second connector portion effective toform an electrically conductive second path from a second front surfaceof said second substrate, wrapping around a portion of an edge of saidsecond substrate, to an opposite second back surface of said secondsubstrate, said second perimeter portion being in electrical contactwith said second connector portion, and wherein said second perimeterportion is peripherally on said second substantial perimeter of saidsecond substrate; and wherein said first front surface and said secondfront surface proximately face each other.
 10. An edge busbar pairaccording to claim 9, wherein said first substantial perimeter iscorrespondingly opposite said second substantial perimeter.
 11. An edgebusbar pair according to claim 9, wherein said first and secondconnector portions each includes a plurality of said electricallyconductive respective first and second paths; and wherein said first andsecond perimeter portions are in electrical contact with said respectiveplurality of electrically conductive first and second paths.
 12. An edgebusbar pair according to claim 11, wherein said plurality of first pathsand said plurality of second paths are in an alternating relation. 13.An edge busbar pair according to claim 12, wherein said first and secondconnector portions have a thickness in the range of from more than onehalf of a gap distance to less than said gap distance; and wherein saidgap distance is the distance separating said first front surface andsaid second front surface.
 14. An edge busbar pair according to claim 9or 11, further including an insulator disposed between said firstsubstrate and said second substrate effective to prevent electricalshorting of said first connector portion to said second connectorportion.
 15. An edge busbar pair according to claim 9, wherein saidfirst and second connector portions and said first and second connectorperimeter portions are composed of aluminum, copper, gold, silver,tungsten, stainless steel, tin, copper/beryllium alloy, indium, nickel,rhodium, nichrome, solder, or a conductive metal oxide.
 16. Anelectrochromic device comprising a first substrate; a second substrate;and an edge busbar pair, wherein said edge busbar pair comprising afirst edge busbar and a second edge busbar, each edge busbar of saidpair peripherally disposed about a respective substantial perimeter edgeof said first substrate and said second substrate respectively, saidedge busbar pair further including: said first busbar comprising a firstconnector portion and a first perimeter portion, said first connectorportion effective to form an electrically conductive first path from afirst front surface of said first substrate, wrapping around a portionof said edge of said first substrate, to an opposite first back surfaceof said first substrate, said first perimeter portion being inelectrical contact with said first connector portion, and wherein saidfirst perimeter portion is peripherally on said first substantialperimeter of said first substrate; a second busbar comprising a secondconnector portion and a second perimeter portion, said second connectorportion effective to form an electrically conductive second path from asecond front surface of said second substrate, wrapping around a portionof an edge of said second substrate, to an opposite second back surfaceof said second substrate, said second perimeter portion being inelectrical contact with said second connector portion, and wherein saidsecond perimeter portion is peripherally on said second substantialperimeter of said second substrate; and wherein said first front surfaceand said second front surface face each other.
 17. An electrochromicdevice according to claim 16, wherein said plurality of first paths andsaid plurality of second paths are in an alternating relation.
 18. Anelectrochromic device according to claim 16, wherein said first andsecond connector portions have a thickness in the range of from morethan one half of a gap distance to less than said gap distance; andwherein said gap distance is the distance separating said firstsubstrate and said second substrate.
 19. An internal busbar for asubstrate having a conductive layer and a reactive layer on a firstsurface, said internal busbar comprising: at least one conductive strip,isolated from chemical reaction with said reactive layer; and at leastone conductive connecting portion, each connecting portion electricallyconnecting a non-peripheral portion of said conductive layer to asegment of said conductive strip.
 20. An internal busbar according toclaim 19, wherein said conductive layer is isolated from chemicalreaction with said reactive layer by a passivation layer.
 21. Aninternal busbar according to claim 19, wherein said at least oneconductive strip is substantially embedded in the substrate.
 22. Aninternal busbar according to claim 19, wherein said at least oneconductive strip is on an opposite second surface of said substrate, andsaid at least one connecting portion extends through said substrate fromsaid first surface to said at least one conductive strip.
 23. Aninternal busbar for a substrate having a conductive layer on a surfaceof the substrate, said internal busbar comprising: at least oneconductive strip having increased electrical conductance per unit lengthfrom the conductive layer in a longitudinal direction of said conductivestrip, and said conductive strip having a perimeter in contact with theconductive layer.
 24. An internal busbar according to claim 23, whereinsaid conductive strip is substantially embedded in the substrate.
 25. Aninternal busbar according to claim 23, wherein said conductive strip isembedded in the substrate, and wherein said conductive strip has alongitudinal surface coextensive with a surface of the conductivesurface layer.
 26. An internal busbar according to claim 23, comprisinga plurality of said conductive strips; and further comprising: at leastone sublayer conductive strip under the conductive layer, said sublayerconductive strip having increased electrical conductance per unit lengthfrom the conductive layer.
 27. An internal busbar according to claim 23,wherein said at least one conductive strip has a transverse axis at anangle to the axis perpendicular to the surface of the substrate.
 28. Aninternal busbar according to claim 27, wherein said transverse axis isparallel to a viewing direction of the substrate.
 29. An internal busbaraccording to claim 28, wherein the substrate is a part of a window, awindshield, a sunroof, a light filter, or a mirror.
 30. An internalbusbar according to claim 23, wherein said at least one conductive stripis composed of a cured metallic frit, conductive ink, conductive epoxy,a metal rod, or a metal bar.
 31. A transparent conducting sheetcomprising: a transparent substrate sheet; a transparent electricallyconducting layer on a substantial surface of said substrate sheet; andat least one conductive strip interior to a perimeter edge of saidconducting layer; said at least on e conductive strip effective to loweran effective conductivity of said conducting layer.
 32. A transparentconducting sheet according to claim 31, further including at least oneedge conductor electrically connected to said transparent conductinglayer on a portion of a peripheral edge of said substrate sheet.
 33. Atransparent conducting sheet according to claim 31, wherein an end ofsaid conductive strip is proximate to said edge conductor, separated bya proximate distance from said edge conductor, and wherein saidproximate distance is electrically bridged by said conducting layer. 34.An electrical device comprising: a conductive layer; an edge conductoron a perimeter portion of said conductive layer; and at least oneconductive strip having increased electrical conductance per unit lengthfrom said conductive layer, and said conductive strip having a perimeterin contact with said conductive layer.
 35. An electrical deviceaccording to claim 36, wherein said at least one conductive strip has anend proximate to said edge conductor.
 36. An electrical device accordingto claim 37, wherein said end and said edge conductor form a gap bridgedby said conductive layer.
 37. A chromogenic device comprising: aplurality of layers responsive to a first signal applied transverselyeffective to cause a change in a first property of said chromogenicdevice, and responsive to a second signal applied in a laminar directioneffective to cause a change in a second property of said chromogenicdevice; at least one conductor strip arranged in said laminar direction,said conductor strip interior of a perimeter of said layers; a firstedge conductor at a first perimeter portion of a first layer of saidlayers; a second edge conductor at a second perimeter portion of asecond layer of said layers; wherein application of said first signaltransversely from said first edge conductor to said second edgeconductor, without application of a potential difference longitudinallyalong said at least one conductor strip, causes a responsive change insaid first property without a change in said second property; andwherein application of said second signal as a longitudinal signal alongsaid at least one conductor strip, without a transverse potentialdifference between said first and second edge conductors, causes aresponsive change in said second property without a change in said firstproperty.
 38. A chromogenic device according to claim 37, wherein saidfirst property is optical transmittance.
 39. A chromogenic deviceaccording to claim 37, wherein said second property is temperature. 40.A method to form an interior busbar comprising the steps of: forming atleast one channel on a surface of a substrate interior to the perimeter;applying a conductive material to said at least one channel; applying aconductive layer over said surface effective to completely cover saidapplied conductive material.
 41. A method to control an electrochromicdevice having a light transmission property that responds to a physicalor chemical effect, wherein the light transmission property changes inresponse to an electrical signal, wherein said method comprises the stepof: intermittently applying the electrical signal by controlling the onduration t₁ and the off duration t₂ of the electrical signalindividually, in response to the physical or chemical effect, effectiveto maintain the light transmission property within a range of about 1%to about 10% of a predetermined value of said light transmissionproperty.
 42. A method according to claim 41, wherein said t₁ and t₂ arecontrolled in response to the physical effect of temperature.
 43. Amethod according to claim 41, wherein at least one of (i) the current,and (ii) the change of current with time, (iii) output fromphotosensors, (iv) charge passed through the device, (v) cell potential,to said electrochromic device is used to respond to the change caused inthe device by the change in temperature; by changing said t₁ and t₂. 44.A method according to claim 41, wherein the temperature of theelectrochromic cell is used to influence the control circuit so as toadjust t₁ and t₂.
 45. An electrochromic device having a lighttransmission property that responds to a physical or chemical property,wherein the light transmission property changes in response to anelectrical signal, wherein said electrochromic device includes: a meansto intermittently apply the electrical signal by controlling the onduration t₁ and the off duration t₂ of the electrical signalindividually, in response to the physical or chemical property,effective to maintain the light transmission property within a range ofabout 1% to about 10% of a predetermined value of the light transmissionproperty.
 46. An electrochromic device according to claim 45, whereinthe means to intermittently apply the electrical signal is a controlcircuit which includes: an astable timer that supplies an input to afirst RC timing circuit; and a monostable timer that supplies an inputto a second RC timing circuit; wherein a first output from the first RCtiming circuit and a second output from the second RC timing circuit isapplied to the electrochromic device.
 47. An electrochromic deviceaccording to claim 46, wherein a microcontroller provides t₁ and t₂. 48.An electrochromic device according to claim 45 or 46, wherein thevoltage of the electrical signal is supplied from a regulated powersupply that is regulated by a switching voltage regulator.
 49. A methodto control an electrochromic device having a light transmission propertythat responds to a physical or chemical property, wherein the lighttransmission property changes in response to an electrical signal,wherein said method comprises the step of: intermittently applying theelectrical signal by controlling the on duration t₁ and the off durationt₂ of the electrical signal individually, in response to the physical orchemical property, effective to maintain the light transmission propertywithin a range of about 1% to about 10% of a predetermined value of saidlight transmission property; wherein the voltage of the appliedelectrical signal is supplied from a regulated power supply that isregulated by a switching voltage regulator.
 50. An electronic circuit topower a chromogenic device wherein the voltage reduction is carried outusing a switching voltage regulator.